I would like to calculate the elastic constants of beta PHB. From this paper. I know that it has P3221 space group. The beta PHB has upward and downward chains, which exist at one lattice site with 50% occupancy, therefore, it is really difficult to do the optimazition in VASP. The structure destroyed with using all the ISIF tags. Has anyone run into the same problem? I'm not sure I did everything right, because I am not an expert in the polymer crystallography.
More or less better results I obtained when I used ISIF=7. My structure was destroyed at the third step. The initial 2 steps gave me the reasonable geometry in CONTCAR. Please find below my INCAR file:
PREC = Accurate
ENCUT = 520
EDIFF = 1e-6
EDIFFG = -0.02
IBRION = 2
ISIF = 7
ISYM = 2
NSW = 50
ISMEAR = 0
SIGMA = 0.1
POTIM = 0.1
PSTRESS = 0.001
NPAR = 4
NSIM = 4
ALGO = Normal
IALGO = 48
ISTART = 0
LPLANE = .TRUE.
LCHARG = .FALSE.
LWAVE = .FALSE.
and POSCAR file:
New structure
1.0
9.2200002670 0.0000000000 0.0000000000
-4.6100001335 7.9847544541 0.0000000000
0.0000000000 0.0000000000 4.6599998474
C O H
24 12 36
Direct
0.459999949 0.990000010 0.669999897
0.010000000 0.469999939 0.336666554
0.530000031 0.540000081 0.003333231
0.990000010 0.459999949 0.330000103
0.469999939 0.010000000 0.663333416
0.540000081 0.530000031 0.996666789
0.349999934 0.970000029 0.919999897
0.029999999 0.379999936 0.586666584
0.620000064 0.650000095 0.253333241
0.970000029 0.349999934 0.080000103
0.379999936 0.029999999 0.413333446
0.650000095 0.620000064 0.746666789
0.349999934 0.930000007 0.409999967
0.070000000 0.419999927 0.076666631
0.580000043 0.650000095 0.743333280
0.930000007 0.349999934 0.590000033
0.419999927 0.070000000 0.923333347
0.650000095 0.580000043 0.256666690
0.279999942 0.089999989 0.899999857
0.910000026 0.189999953 0.566666543
0.810000062 0.720000029 0.233333185
0.089999989 0.279999942 0.100000143
0.189999953 0.910000026 0.433333486
0.720000029 0.810000062 0.766666830
0.439999938 0.009999998 0.179999948
0.990000010 0.429999948 0.846666634
0.570000052 0.560000062 0.513333261
0.009999998 0.439999938 0.820000052
0.429999948 0.990000010 0.153333381
0.560000062 0.570000052 0.486666709
0.199999973 0.829999983 0.409999967
0.170000002 0.369999975 0.076666631
0.629999995 0.800000012 0.743333280
0.829999983 0.199999973 0.590000033
0.369999975 0.170000002 0.923333347
0.800000012 0.629999995 0.256666690
0.559999883 0.119999982 0.639999866
0.879999995 0.439999908 0.306666523
0.560000122 0.440000117 0.973333180
0.119999982 0.559999883 0.360000134
0.439999908 0.879999995 0.693333447
0.440000117 0.560000122 0.026666800
0.519999862 0.909999967 0.709999859
0.090000004 0.609999895 0.376666516
0.390000135 0.480000138 0.043333191
0.909999967 0.519999862 0.290000141
0.609999895 0.090000004 0.623333454
0.480000138 0.390000135 0.956666827
0.239999965 0.840000033 0.919999897
0.159999996 0.399999976 0.586666584
0.600000024 0.760000050 0.253333241
0.840000033 0.239999965 0.080000103
0.399999976 0.159999996 0.413333446
0.760000050 0.600000024 0.746666789
0.189999968 0.059999991 0.719999909
0.939999998 0.129999980 0.386666566
0.870000005 0.810000062 0.053333241
0.059999991 0.189999968 0.280000091
0.129999980 0.939999998 0.613333404
0.810000062 0.870000005 0.946666777
0.209999964 0.089999989 0.100000024
0.910000026 0.119999975 0.766666710
0.879999995 0.790000021 0.433333367
0.089999989 0.209999964 0.899999976
0.119999975 0.910000026 0.233333305
0.790000021 0.879999995 0.566666663
0.379999936 0.219999969 0.869999886
0.780000031 0.159999967 0.536666572
0.840000033 0.620000064 0.203333214
0.219999969 0.379999936 0.130000114
0.159999967 0.780000031 0.463333458
0.620000064 0.840000033 0.796666801
Thank you in advance!
ISIFtags, would you consider to show us an input file in acodeblock? This can substantially help you get an answer. $\endgroup$