kptgen : accuracy of atomic positions

When I used KPTGEN today (May 27, 1999), I had a curious experience.
(In fact, no curious... Only I might have not realized the following.)

If I use the following input for "kptgen", it fails.

7.1431642 7.1431642 12.402272 acell
0.8660254037844386 0.5 0 -0.8660254037844386 0.5 0 0 0 1 rprim
5 3 natom, ntype
1 2 2 3 3
0.00000 0.00000 0.00000
0.33333 0.66667 0.29000
0.66667 0.33333 0.71000
0.33333 0.66667 0.64000
0.66667 0.33333 0.36000
0 0 ibrav, inpgd
0 nkpt
4 4 4 0 0 0 Monkhorst-Pack indices and origin for grid

cpointg error: atom 2 doesn't fit symmetry 2
rotated coord -2.062033266329 -3.571617815821 3.596658880000
other atom 2.062095127946 3.571582100000 8.805613120000
difference -4.124128394275 -7.143199915821 -5.208954240000
phases -.500036275549 -.499981861897 -.876306680044
rotation matrix: -.50 -.87 .00 .87 -.50 .00 .00 .00 1.00
nonsymmorphic transl: .000000000000 .000000000000 .000000000000

But If I use the following input (the digits of "xred" are increased),

7.1431642 7.1431642 12.402272 acell
0.8660254037844386 0.5 0 -0.8660254037844386 0.5 0 0 0 1 rprim
5 3 natom, ntype
1 2 2 3 3
0.000000000 0.000000000 0.000000000
0.333333333 0.666666667 0.290000000
0.666666667 0.333333333 0.710000000
0.333333333 0.666666667 0.640000000
0.666666667 0.333333333 0.360000000
0 0 ibrav, inpgd
0 nkpt
4 4 4 0 0 0 Monkhorst-Pack indices and origin for grid

Thus I really realized that the digits of "xred" is very important and that enough digits of "xred" are prepared in all the input examples

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Masayoshi Mikami
Mitsubishi Chemical Corporation (Research and Development Division, Yokohama Research Center)
Phone: +81-45-963-3265 Fax:+81-45-963-3947
E-mail: mmikami@rc.m-kagaku.co.jp (office), mmikami@yk.rim.or.jp (home)
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