ABINIT, PAW input variables:

List and description.


This document lists and provides the description of the name (keywords) of the input variables for runs based on the Projector Augmented Waves methodology, to be used in the main input file of the abinit code.

Content of the file : alphabetical list of PAW input variables.


A.
B. bxctmindg  
C.
D. dmatpawu   dmatpuopt   dmatudiag  
E.
F. f4of2_sla   f6of2_sla  
G.
H.
I. iboxcut  
J. jpawu  
K.
L. lexexch   lpawu  
M. mqgriddg  
N. ngfftdg  
O.
P. pawcpxocc   pawcross   pawecutdg   pawfatbnd   pawlcutd   pawlmix   pawmixdg   pawnhatxc   pawnphi   pawntheta   pawnzlm   pawoptmix   pawoptosc   pawovlp   pawprtden   pawprtdos   pawprtvol   pawprtwf   pawspnorb   pawstgylm   pawsushat   pawusecp   pawxcdev   prtefg   prtfc   prtnabla   ptcharge  
Q. quadmom  
R.
S. spnorbscl  
T.
U. upawu   usedmatpu   useexexch   usepawu   usepotzero   usexcnhat  





bxctmindg
Mnemonics: BoX CuT-off MINimum for the Double Grid (PAW)
Characteristic:
Variable type: real
Default is 2.0

Only relevant if usepaw==1

The box cut-off ratio is the ratio between the wavefunction plane wave sphere radius, and the radius of the sphere that can be inserted in the FFT box, in reciprocal space.
If the density was generated only from wavefunctions, this ratio should be at least two in order for the density to be exact. If one uses a smaller ratio, one will gain speed, at the expense of accuracy. In case of pure ground state calculation (e.g. for the determination of geometries), this is sensible. However, the wavefunctions that are obtained CANNOT be used for starting response function calculation.
However, some augmentation charge is always added in PAW, and even with the box cut-off ratio larger than two, the density is never exact. Sometimes, this ratio must be much larger than two for the computation to be converged at the required level of accuracy.





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dmatpawu
Mnemonics: initial Density MATrix for PAW+U
Characteristic:
Variable type: real(2*max(lpawu)+1,2*max(lpawu)+1,max(nsppol, nspinor),natpawu)
Default is *-10.0

Only relevant if usepaw==1 and usepawu==1 and usedmatpu!=0

For Ground state calculations only.
Gives the value of an initial density matrix used in LDA+U and kept fixed during the first abs(usedmatpu) SCF iterations.
Only components corresponding to lpawu angular momentum are requested.
Restriction: In order to use dmatpawu, lpawu must be identical for all atom types (or -1).
The occupation matrix is in the basis of real spherical harmonics Slm (note that this differs from the choice made when prtdosm=1 , that is in the basis of complex spherical harmonics). Their are ordered by increasing m, and are defined e.g. in the article "Evaluation of the rotation matrices in the basis of real spherical harmonics", by Miguel A. Blancoa, M. Floreza, M. Bermejo, Journal of Molecular Structure (Theochem) 419, 19 (1997), that can be downloaded from the author Web site . For the case l=2 (d states), the five columns corresponds respectively to (the normalisation factor has been dropped)


dmatpawu must always be given as a "spin-up" occupation matrix (and eventually a "spin-down" matrix). Be aware that its physical meaning depends on the magnetic properties imposed to the system (with nsppol, nspinor, nspden):





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dmatpuopt
Mnemonics: Density MATrix for PAW+U OPTion
Characteristic:
Variable type: integer
Default is 2

Only relevant if usepaw==1 and usepawu==1

This option governs the way occupations of localized atomic levels are computed:

In the general case dmatpuopt=2 is suitable. The use of dmatpuopt=1 is restricted to PAW datasets in which the first atomic wavefunction of the correlated subspace is a normalized atomic eigenfunction.





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dmatudiag
Mnemonics: Density MATrix for paw+U, DIAGonalization
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1 and usepawu==1 and nspden != 4

Relevant only for Ground-State calculations.
This option can be used to diagonalize the occupation matrix Nocc_{m,m_prime}.
Relevant values are:





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f4of2_sla
Mnemonics: F4 Over F2 ratio of Slater integrals
Characteristic:
Variable type: real
Default is ['0.625 for d electron', '0.6681 for f electron']

Only relevant if usepaw==1 and (usepawu==1 or usedmft==1)

This gives the ratio of Slater Integrals F4 and F2. It is used in DFT+U or DFT+DMFT for the calculation of the orbital dependent screened coulomb interaction.





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f6of2_sla
Mnemonics: F6 Over F2 ratio of Slater integrals
Characteristic:
Variable type: real
Default is 0.4943

Only relevant if (usepawu==1 or usedmft==1) and lpawu=3

Gives the ratio of Slater Integrals F6 and F2. It is used with f4of2_sla==3 in DFT+U or DFT+DMFT for the calculation of the orbital dependent screened coulomb interaction.





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iboxcut
Mnemonics: Integer governing the internal use of BOXCUT - not a very good choice of variable name
Characteristic:
Variable type: integer
Default is 0

Concern all summations in the reciprocal space and is allowed in PAW and norm-conserving.





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jpawu
Mnemonics: value of J for PAW+U
Characteristic: ENERGY
Variable type: real(ntypat)
Default is *0

Only relevant if usepaw==1 and usepawu==1

Gives the value of the screened exchange interaction between correlated electrons corresponding to lpawu for each species.
In the case where lpawu =-1, the value is not used.





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lexexch
Mnemonics: value of angular momentum L for EXact EXCHange
Characteristic:
Variable type: integer(ntypat)
Default is -1

Only relevant if useexexch==1

Give for each species the value of the angular momentum (only values 2 or 3 are allowed) on which to apply the exact exchange correction.





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lpawu
Mnemonics: value of angular momentum L for PAW+U
Characteristic:
Variable type: integer(ntypat)
Default is *-1

Only relevant if usepawu==1 or usepawu== 2

Give for each species the value of the angular momentum (only values 2 or 3 are allowed)  on which to apply the LDA+U correction.





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mqgriddg
Mnemonics: Maximum number of Q-wavevectors for the 1-dimensional GRID for the Double Grid in PAW
Characteristic: DEVELOP
Variable type: integer
Default is 3001

Maximum number of wavevectors used to sample the local part of the potential, in PAW. Actually referred to as mqgrid_vl internally. Should change name to the latter ... See also mqgrid





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ngfftdg
Mnemonics: Number of Grid points for Fast Fourier Transform : Double Grid
Characteristic:
Variable type: integer(3)
Default is [0, 0, 0]

Only relevant if usepaw==1

This variable has the same meaning as ngfft (gives the size of fast Fourier transform (fft) grid in three dimensions) but concerns the "double grid" only used for PAW calculations.





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pawcpxocc
Mnemonics: PAW - use ComPleX rhoij OCCupancies
Characteristic:
Variable type: integer
Default is 2 if optdriver==0 and ionmov<6 and pawspnorb==1 and iscf>=10 and (kptopt !=1 or kptopt!=2) and usepaw==1, 1 otherwise.

Only relevant if usepaw==1

The only possible values for pawcpxocc are 1 or 2.
When pawcpxocc==1 , "direct" decomposition of total energy cannot be printed out.
When pawcpxocc==2 , PAW augmentation occupancies are treated as COMPLEX; else they are considered as REAL.
This is needed when time-reversal symmetry is broken (typically when spin-orbit coupling is activated).

Note for ground-state calculations (optdriver=0):
The imaginary part of PAW augmentation occupancies is only used for the computation of the total energy by "direct scheme"; this is only necessary when SCF mixing on potential is chosen (iscf<10).
When SCF mixing on density is chosen (iscf>=10), the "direct" decomposition of energy is only printed out without being used. It is thus possible to use pawcpxocc=1 in the latter case.
In order to save CPU time, when molecular dynamics is selected (ionmov>=6) and SCF mixing done on density (iscf>=10), pawcpxocc=2 is (by default) set to 1





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pawcross
Mnemonics: PAW - add CROSS term in oscillator strengths
Characteristic:
Variable type: integer
Default is 0

Only relevant if (optdriver==3 or optdriver==4) and usepaw==1

When pawcross=1 , the overlap between the plane-wave part of one band and the on-site part of an other is taken into account in the computation of the oscillator strengths. Hence, the completeness of the on-site basis is no longer assumed.





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pawecutdg
Mnemonics: PAW - Energy CUToff for the Double Grid
Characteristic: ENERGY
Variable type: real
Default is -1 (Comment: pawecutdg MUST be specified for PAW calculations.)

Only relevant if usepaw==1

Define the energy cut-off for the fine FFT grid (the "double grid", that allows to transfer data from the normal, coarse, FFT grid to the spherical grid around each atom).
pawecutdg must be larger or equal to ecut. If it is equal to it, then no fine grid is used. The results are not very accurate, but the computations proceed quite fast.
For typical PAW computations, where ecut is on the order of 15 Ha, pawecutdg must be tested according to what you want to do. For calculations that do not require a high accuracy (molecular dynamics for instance) a value of 20 Ha is enough. For calculations that require a high accuracy (response fonctions for instance) it should be on the order of 30 Ha. Choosing a larger value should not increase the accuracy, but does not slow down the computation either, only the memory. The choice made for this variable DOES have a bearing on the numerical accuracy of the results, and, as such, should be the object of a convergence study. The convergence test might be made on the total energy or derived quantities, like forces, but also on the two values of the "Compensation charge inside spheres", a quantity written in the log file.





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pawfatbnd
Mnemonics: PAW: print band structure in the FAT-BaND representation
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1

For Ground-State calculations and non self-consistent calculations only.
This option can be used to plot band structure. For each atom (specified by natsph and iatsph), each angular momentum, and each spin polarisation, the band structure is written in files (such as e.g. FATBANDS_at0001_Ni_is2_l2_m-1). Each file contains the eigenvalue, and the contribution of angular momentum L, and projection of angular momentum M, (for the corresponding wavefunction) to the PAW density inside the PAW sphere as a function of the index of the k-point. The output can be readily plotted with the software xmgrace (e.g xmgrace FATBANDS_at0001_Ni_is2_l2_m-1). Relevant values are:





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pawlcutd
Mnemonics: PAW - L angular momentum used to CUT the development in moments of the Densitites
Characteristic:
Variable type: integer
Default is 10

Only relevant if usepaw==1

The expansion of the densities in angular momenta is performed up to l=pawlcutd.
Note that, for a given system, the maximum value of pawlcutd is 2*l_max , where l_max is the maximum l of the PAW partial waves basis.

The choice made for this variable DOES have a bearing on the numerical accuracy of the results, and, as such, should be the object of a convergence study. The convergence test might be made on the total energy or derived quantities, like forces, but also on the two values of the "Compensation charge inside spheres", a quantity written in the log file.





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pawlmix
Mnemonics: PAW - maximum L used in the spherical part MIXing
Characteristic:
Variable type: integer
Default is 10

Only relevant if usepaw==1

The choice made for this variable determine how the spherical part of the density is mixed during electronic iterations.

Only parts of rhoij quantities associated with l angular momenta up to l=pawlmix are mixed. Other parts of augmentation occupancies are not included in the mixing process.
This option is useful to save CPU time but DOES have a bearing on the numerical accuracy of the results.





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pawmixdg
Mnemonics: PAW - MIXing is done (or not) on the (fine) Double Grid
Characteristic:
Variable type: integer
Default is 0 if npfft==1, 1 otherwise.

Only relevant if usepaw==1

The choice made for this variable determines the grid on which the density (or potential) is mixed during the SCF cycle.

- If pawmixdg=1 the density/potential is mixed in REAL space using the fine FFT grid (defined by pawecutdg or ngfftdg).
- If pawmixdg=0 the density/potential is mixed in RECIPROCAL space using the coarse FFT grid (defined by ecut or ngfft). Only components of the coarse grid are mixed using the scheme defined by iscf; other components are only precondionned by diemix and simply mixed.
This option is useful to save memory and does not affect numerical accuracy of converged results. If pawmixdg=1 , density and corresponding residual are stored for previous iterations and are REAL arrays of size nfftdg. If pawmixdg=0 , density and corresponding residual are stored for previous iterations and are COMPLEX arrays of size nfft. The memory saving is particularly efficient when using the Pulay mixing (iscf=7 or 17).

In wavelet calculations usewvl=1:
- pawmixdg is set to 1 by default.
- A value of 0 is not allowed.
- Density/potential is mixed in REAL space (Here only one grid is used).





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pawnhatxc
Mnemonics: PAW - Flag for exact computation of gradients of NHAT density in eXchange-Correlation.
Characteristic:
Variable type: integer
Default is 1

Only relevant if usepaw==1

Relevant only when a GGA exchange-correlation functional is used.
When this flag is activated, the gradients of compensation charge density (n_hat) are exactly computed (i.e. analytically); when it is deactivated, they are computed with a numerical scheme in reciprocal space (which can produce inaccurate results if the compensation charge density is highly localized).
As analytical treatment of compensation charge density gradients is CPU time demanding, it is possible to bypass it with pawnhatxc=0; but the numerical accuracy can be affected by this choice. It is recommended to test the validity of this approximation before use.





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pawnphi
Mnemonics: PAW - Number of PHI angles used to discretize the sphere around each atom.
Characteristic:
Variable type: integer
Default is 13

Only relevant if usepaw==1

Number of phi angles (longitude) used to discretize the data on the atomic spheres. This discretization is completely defined by pawnphi and pawntheta.





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pawntheta
Mnemonics: PAW - Number of THETA angles used to discretize the sphere around each atom.
Characteristic:
Variable type: integer
Default is 12

Only relevant if usepaw==1

Number of theta angles (latitude) used to discretize the data on the atomic spheres. This discretization is completely defined by pawntheta and pawnphi.





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pawnzlm
Mnemonics: PAW - only compute Non-Zero LM-moments of the contributions to the density from the spheres
Characteristic:
Variable type: integer
Default is 1

Only relevant if usepaw==1

Concerns the computation of the contributions to the density from the spheres (named rho_1 - rho_tild_1).
If set to 0, all lm-moments of the sphere contributions to the density are computed at each electronic iteration.
If set to 1, only non-zero lm-moments of the sphere contributions to the density are computed at each electronic iteration (they are all computed at the first iteration then only those found to be non-zero will be computed ; thus the first iteration is more cpu intensive)





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pawoptmix
Mnemonics: PAW - OPTion for the MIXing of the spherical part
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1

In the case of PAW computations, during the self-consistent cycle, ABINIT mixes the density ρ(r)= ρ(r) +ρ(r) and the occupancy matrix ρij. (ρ(r) is the pseudo density, ρ(r) is the compensation charge density). It can be redundant as ρij is contained in ρ(r).

This has only an influence on the efficiency of the mixing algorithm.
In cas of mixing problems, the first suggestion is to increase the size of the history (see npulayit). Then it is also possible to play with the parameters of the Kerker mixing: diemix, diemac, etc...





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pawoptosc
Mnemonics: PAW - OPTion for the computation of the OSCillator matrix elements
Characteristic:
Variable type: integer
Default is 0

Only relevant for GW or BETHE_SALPETER calculations with PAW.
This variable defines the approach used for the evaluation of the oscillator matrix elements within the PAW formalism. Possible values are 0,1,2.
If pawoptosc=0 the code uses its internal default value (2 for SCREENING calculations, 1 for SIGMA calculations, 2 for BETHE_SALPETER)
If pawoptosc=1 the matrix elements are computed with the expression given by Arnaud and Alouani in PRB 62. 4464 The equation is exact provided that the set of PAW partial waves is complete.
If pawoptosc=2 the matrix elements are computed with the approximated expression proposed by Shishkin and Kresse in PRB 74. 035101





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pawovlp
Mnemonics: PAW - spheres OVerLap allowed (in percentage)
Characteristic:
Variable type: real
Default is 5.0

Only relevant if usepaw==1

When PAW is activated, a localized atomic basis is added to describe wave functions. Spheres around atoms are defined and they are IN PRINCIPLE not allowed to overlap. However, a small overlap can be allowed without compromising the accuracy of results. Be aware that too high overlaps can lead to unphysical results.
With the pawovlp variable, the user can control the (voluminal) overlap percentage allowed without stopping the execution.
pawovlp is the value (in percentage: 0...100%) obtained by dividing the volume of the overlap of two spheres by the volume of the smallest sphere.
The following values are permitted for pawovlp:

- pawovlp<0. : overlap is always allowed
- pawovlp=0. : no overlap is allowed
- pawovlp>0. and <100. : overlap is allowed only if it is less than pawovlp %





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pawprtden
Mnemonics: PAW: PRinT total physical electron DENsity
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1

Deprecated : See the prtden.





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pawprtdos
Mnemonics: PAW: PRinT partial DOS contributions
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1 and prtdos==3

This input variable controls the computation and/or printing of contributions to the PAW partial DOS in _DOS file(s):

+ Plane-waves contribution
+ "on-site" all-electron contribution (phi)
- "on-site" pseudo contribution (phi_tild).
If pawprtdos=0:
- The 3 contributions are computed; only the total partial DOS is output in _DOS file.
If pawprtdos=1:
- The 3 contributions are computed and output in _DOS file.
- In that case, integrated DOS is not output.
If pawprtdos=2:
- Only "on-site" all-electron contribution is computed and output in _DOS file.
- This a (very) good approximation of total DOS, provided that (1) the PAW local basis is complete, (2) the electronic charge is mostly contained in PAW spheres.
- In that case, the ratsph variable is automatically set to the PAW radius.





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pawprtvol
Mnemonics: PAW: PRinT VOLume
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1

Control print volume and debugging output for PAW in log file or standard output. If set to 0, the print volume is at its minimum.
pawprtvol can have values from -3 to 3:
- pawprtvol=-1 or 1: matrices rho_ij (atomic occupancies) and D_ij (psp strength) are printed at each SCF cycle with details about their contributions.
- pawprtvol=-2 or 2: like -1 or 1 plus additional printing: moments of "on-site" densities, details about local exact exchange.
- pawprtvol=-3 or 3: like -2 or 2 plus additional printing: details about PAW+U, rotation matrices of sphercal harmonics.
When pawprtvol>=0, up to 12 components of rho_ij and D_ij matrices for the 1st and last atom are printed.
When pawprtvol<0, all components of rho_ij and D_ij matrices for all atoms are printed.





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pawprtwf
Mnemonics: PAW: PRinT WaveFunctions
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1

This input variable controls the output of the full PAW wave functions including the on-site contribution inside each PAW sphere needed to reconstruct the correct nodal shape in the augmentation region. pawprtwf=1 causes the generation of a file _AE_WFK that contains the full wavefunctions in real space on the fine FFT grid defined by pawecutdg or ngfftdg. Limitations: At present (v6.0), pawprtwf=1 is not compatible neither with the k-point parallelism nor with the parallelism over G-vectors. Therefore the output of the _AE_WFK has to be done in sequential. Moreover, in order to use this feature, one has to enable the support for ETSF-IO at configure-time as the _AW_WFK file is written using the NETCDF file format following the ETSF-IO specification for wavefunctions in real space. If the code is run entirely in serial, additional output is made of various contributions to the all-electron wavefunction. By default the full available set of bands and k-points are ouput, but a single band and k-point index can be requested by using the variables pawprt_b and pawprt_k.





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pawspnorb
Mnemonics: PAW - option for SPiN-ORBit coupling
Characteristic:
Variable type: integer
Default is 1 if nspinor==2, 0 otherwise.

Only relevant if usepaw==1

When PAW is activated, the spin-orbit coupling can be added without the use of specific PAW datasets (pseudopotentials).
If pawspnorb=1, spin-orbit will be added.
If the wavefunction is spinorial (that is, if nspinor=2), there is no reason not to include the spin-orbit interaction, so that the default value of pawspnorb becomes 1 when nspinor=2.
Note that only the all-electron "on-site" contribution to the Hamiltonian is taken into account; this is a very good approximation but requires the following conditions to be fullfilled:

1- the ~ φ i basis is complete enough
2- the electronic density is mainly contained in the PAW sphere

Also note that, when spin-orbit coupling is activated and there is some magnetization nspden=4, the time-reversal symmetry is broken.
The use of kptopt=1 or kptopt=2 is thus forbidden. It is advised to use kptopt=3 (no symmetry used to generate k-points) or kptopt=4 (only spatial symmetries used to generate k-points).
Be careful if you choose to use kptopt=0 (k-points given by hand); Time-reversal symmetry has to be avoided.
An artificial scaling of the spin-orbit can be introduced thanks to the spnorbscl input variable.





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pawstgylm
Mnemonics: PAW - option for the STorage of G_l(r).YLM(r)
Characteristic:
Variable type: integer
Default is 1

Only relevant if usepaw=1

When PAW is activated, the computation of compensation charge density (so called "hat" density) requires the computation of g_l(r).Y_lm(r) factors (and cartesian derivatives) at each point of real space contained in PAW spheres. The number of atoms, of (l,m) quantum numbers and the sharpness of the real FFT grid can lead to a very big {g_l.Y_lm} datastructure. One can save memory by putting pawstgylm=0; but, in that case, g_l(r).Y_lm(r) factors a re-computed each time they are needed and CPU time increases.

Possible choices:
- pawstgylm=0 : g_l(r).Y_lm(r) are not stored in memory and recomputed.
- pawstgylm=1 : g_l(r).Y_lm(r) are stored in memory.

Note:
g_l(r) are shape functions (analytically known)
Y_lm(r) are real spherical harmonics





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pawsushat
Mnemonics: PAW - SUSceptibility, inclusion of HAT (compensation charge) contribution
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1 and optdriver==0

Ground-State calculation only.
When a sophisticated preconditioning scheme is selected for the SCF cycle of a Ground-State calculation (iprcel>0), the computation of the susceptibility matrix is required several times during the cycle. This computation is computer time consuming, especially -- within PAW -- because of the inclusion of additional terms due to the compensation charge density. As only a crude valuation of the susceptibilty matrix is needed (to evaluate a preconditioning matrix), the compensation charge contribution can be neglected to save CPU time (select pawsushat=0). This approximation could be unfavourable in some cases; in the latter, we advise to put pawsushat=1.

Possible choices:
- pawsushat=0 : only plane-wave contribution to suscep. matrix is computed.
- pawsushat=1 : the whole suscep. matrix (PW + PAW on-site) is computed.





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pawusecp
Mnemonics: PAW - option for the USE of CPrj in memory (cprj=WF projected with NL projector)
Characteristic:
Variable type: integer
Default is 1

Only relevant if usepaw==1


When PAW is activated, the computation of cprj arrays is memory and time consuming.
When pawusecp=0, then the cprj are never kept in memory, they are recomputed when needed (this is CPU-time consuming). When pawusecp=1, then the cprj are computed once and then kept in memory.
Change the value of the keyword only if you are an experienced user (developper).
Remember: cprj = (WF_n .dot. p_i) (WF_n=wave function, p_i=non-local projector).

For the time being, only activated for RF calculations.





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pawxcdev
Mnemonics: PAW - choice for eXchange-Correlation DEVelopment (spherical part)
Characteristic:
Variable type: integer
Default is 1

Only relevant if usepaw==1


Be careful: GGA requires pawxcdev > 0





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prtefg
Mnemonics: PRint Electric Field Gradient
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1, quadmom





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prtfc
Mnemonics: PRinT Fermi Contact term
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1





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prtnabla
Mnemonics: PRint NABLA
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1





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ptcharge
Mnemonics: PoinT CHARGEs
Characteristic:
Variable type: real(ntypat)
Default is *0

Only relevant if usepaw==1 and prtefg>=3






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quadmom
Mnemonics: QUADrupole MOMents
Characteristic:
Variable type: real(ntypat)
Default is *0

Only relevant if usepaw==1 and prtefg>=1





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spnorbscl
Mnemonics: SPin-ORBit SCaLing
Characteristic:
Variable type: real
Default is 1.0

Only relevant if usepaw==1 and pawspnorb>= 1

Scaling of the spin-orbit interaction. The default values gives the first-principles value, while other values are used for the analysis of the effect of the spin-orbit interaction, but are not expected to correspond to any physical situation.





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upawu
Mnemonics: value of U for PAW+U
Characteristic: ENERGY
Variable type: real(ntypat)
Default is *0

Only relevant if usepaw==1 and usepawu==1

Gives the value of the screened coulomb interaction between correlated electrons corresponding to lpawu for each species.
In the case where lpawu =-1, the value is not used.
In the case of a GW calculation, the U interaction defined by upawu will be REMOVED from the self energy. In particular, for G0 W0 calculations (perturbative calculations), the energy eigenvalues obtained after an underlying DFT+U calculation will be
E_GW = E_DFT+U + < phi | Self-energy - U | phi>
Actually, in order to perform a GW @ DFT+U calculation, one should define the same value of U in the self-energy calculation, than the one defined in the DFT calculation. The easiest is actually to define the value of U for the whole set of calculations (for the different datasets), including the screening, even if the U value does not play explicitly a role in the computation of the latter (well, the input wavefunctions will be different anyhow).
It is possible to perform calculations of the type GW+U_prime @ DFT+U , so keeping a U interaction (usually smaller than the initial U) in the GW calculation, by defining a smaller U than the one used in the DFT calculation. This value will be subtracted in the GW correction calculation, as outlined above.
Explicitly, in order to do a calculation of a material with a DFT U value of 7.5 eV, followed by a GW calculation where there is a residual U value of 2 eV, one has to define :

  uldau1   7.5 eV   ! This is for the DFT calculation
...
optdriver4  4
uldau4   5.5 eV   ! This is for the screening calculation
 





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usedmatpu
Mnemonics: USE of an initial Density MATrix in Paw+U
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1 and usepawu==1

When usedmatpu/=0, an initial density matrix (given by dmatpawu keyword) is used and kept fixed during the first ABS(usedmatpu) SCF steps.
This starting value of the density matrix can be useful to find the correct ground state. Within LDA+U formalism, finding the minimal energy of the system is tricky; thus it is advised to test several values of the initial density matrix.
Note also that the density matrix has to respect some symmetry rules determined by the space group. If the symmetry is not respected in the input, the matrix is however automatically symmetrised.

The sign of usedmatpu has influence only when ionmov/=0 (dynamics or relaxation):
- When usedmatpu>0, the density matrix is kept constant only at first ionic step
- When usedmatpu<0, the density matrix is kept constant at each ionic step





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useexexch
Mnemonics: USE of EXact EXCHange
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1

When useexexch=1, the hybrid functional PBE0 is used in PAW, inside PAW spheres only, and only for correlated orbitals given by lexexch. To change the ratio of exact exchange, see also exchmix.





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usepawu
Mnemonics: USE PAW+U (spherical part)
Characteristic:
Variable type: integer
Default is 0

Only relevant if usepaw==1

Must be non-zero if a DFT+U calculation is done, or if a GW calculation following a DFT+U calculation is done (important !).

If LDA+U is activated (usepawu=1 or 2), the lpawu, upawu and jpawu input variables are read.
The implementation is done inside PAW augmentation regions only (cf Ref [4]). The initial density matrix can be given in the input file (see usedmatpu). The expression of the density matrix is chosen thanks to dmatpuopt. See also How_to_use_LDA_plus_U.txt . for some informations.
In the case of a GW calculation on top of a DFT+U, the absence of definition of a U value in the self-energy will LEAVE the underlying U from the DFT calculation. Thus, the code will actually do a GW+U @ DFT+U calculation. Note that the screening calculation will not be affected by the presence/absence of a U value.
Actually, in order to perform a GW @ DFT+U calculation, one should define the same value of U in the self-energy calculation, than the one defined in the DFT calculation. The code will know that the interaction corresponding to that value has to be SUBTRACTED inside the self-energy. The easiest is actually to define the presence of U for the whole set of calculations (for the different datasets), including the screening, even if the U value does not play explicitly a role in the computation of the latter (well, the input wavefunctions will be different anyhow).
It is possible to perform calculations of the type GW+U_prime @ DFT+U , so keeping a smaller U interaction in the GW calculation, by subtracting a smaller U than the one used in the DFT calculation. See the description of the upawu input variable.
References:
[1] V. I. Anisimov, J. Zaanen, and O. K. Andersen PRB 44, 943 (1991)
[2] A.I. Lichtenstein, V.I. Anisimov and J. Zaanen PRB 52, 5467 (1995)
[3] M. T. Czyzyk and G. A. Sawatzky PRB 49, 14211 (1994)
[4] O. Bengone, M. Alouani, P. Blochl, and J. Hugel PRB 62, 16392 (2000)


Suggested acknowledgment:
- B. Amadon, F. Jollet and M. Torrent, Phys. Rev. B 77, 155104 (2008).





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usepotzero
Mnemonics: USE POTential ZERO
Characteristic:
Variable type: integer
Default is 0





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usexcnhat
Mnemonics: USE eXchange-Correlation with NHAT (compensation charge density)
Characteristic:
Variable type: integer
Default is -1

Only relevant if usepaw==1


This flag determines how the exchange-correlation terms are computed for the pseudo-density.
When usexcnhat=0, exchange-correlation potential does not include the compensation charge density, i.e. Vxc=Vxc(tild_Ncore + tild_Nvalence).
When usexcnhat=1, exchange-correlation potential includes the compensation charge density, i.e. Vxc=Vxc(tild_Ncore + tild_Nvalence + hat_N).
When usexcnhat=-1,the value of usexcnhat is determined from the reading of the PAW dataset file (pseudopotential file). When PAW datasets with different treatment of Vxc are used in the same run, the code stops.





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