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liutao_jlu822

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[交流] 动力学NPT压力

最近用vasp 5.2.12做NPT的MD模拟以下是INCAR
ISTART = 0
INIWAV = 1

ISYM = 0

ENCUT = 800
ENAUG = 2400
PREC = high
MAXMIX = 40
EDIFF = 0.001
NELMIN = 4

ISMEAR = -1
SIGMA = 0.172

IBRION = 0
LREAL = .FALSE.

ALGO = Very Fast

NSW = 1000

LCHARG = .FALSE.
LWAVE = .TURE.
TEBEG = 2000.0
TEEND = 2000.0

SMASS = 0
NBLOCK = 50
POTIM = 1.0

PSTRESS = 1500
ISIF = 3

PMASS = 20

DMALGO = 3
LANGEVIN_GAMMA = 50,50,50
LANGEVIN_GAMMA_L = 50

提取OUTCAT中stress信息如下

in kB 4172.66112 3902.39396 4400.48371 0.75775 0.00033 -0.00129
in kB 4175.23568 3903.55126 4397.35739 -1.09890 4.17513 0.79122
in kB 4177.58431 3902.41118 4388.94827 -1.87095 8.17570 1.01140
in kB 4180.84173 3901.55583 4377.15279 -2.23297 11.91227 0.64589
in kB 4183.17536 3899.89882 4361.25600 -1.97631 15.42282 -0.17552
in kB 4184.61089 3897.95280 4341.75406 -1.03387 18.65903 -1.31153
in kB 4184.97713 3895.89317 4319.14836 0.60726 21.60255 -2.56697
in kB 4183.96156 3893.68236 4293.78485 2.78659 24.21068 -3.74790
in kB 4181.50387 3891.18446 4266.20603 5.28728 26.42985 -4.67963
in kB 4177.77326 3888.18529 4237.08118 7.81475 28.20301 -5.22024
in kB 4173.13620 3884.51263 4207.21849 10.00879 29.47044 -5.27320

我的问题是
为什么设置PSTRESS = 1500，但是OUTCAR却给出压力在4000左右？

如果只是普通的结构优化，设置IBRION = 2，stress信息如下

in kB 4164.18638 3891.83071 4390.16931 -0.00023 0.00009 0.00002
in kB 3839.38224 3590.92924 4038.54882 0.00163 -0.00007 -0.00002
in kB 2996.27502 2807.91069 3130.59147 -0.00024 -0.00002 -0.00013
in kB 1778.69087 1669.38225 1831.87127 -0.00002 0.00001 -0.00004
in kB 1497.67446 1404.55014 1534.81292 0.00048 -0.00002 0.00006
in kB 1448.12627 1357.76865 1482.58460 0.00035 0.00002 -0.00004
in kB 1449.96058 1361.96624 1487.14790 0.00273 0.00009 0.00010
in kB 1456.56412 1374.89207 1499.80704 0.00234 -0.00000 0.00001
in kB 1477.63406 1406.94473 1524.00978 -0.00029 -0.00005 0.00003
in kB 1548.88679 1500.03893 1572.79441 -0.00230 -0.00005 0.00007
in kB 1803.80977 1850.93418 1743.05711 -0.00311 0.00001 0.00025

....

in kB 1500.08061 1499.76833 1499.91247 0.00031 -0.00003 -0.00000
in kB 1499.86822 1499.56459 1499.69498 -0.00016 -0.00000 0.00002
in kB 1499.96526 1499.79712 1500.02728 0.00052 -0.00003 0.00000
in kB 1500.17449 1500.27199 1500.67246 0.00043 -0.00001 -0.00002
in kB 1499.88523 1500.04832 1500.34787 -0.00023 -0.00001 -0.00003
in kB 1499.30292 1499.59149 1499.70567 -0.00008 -0.00000 -0.00003
in kB 1499.58503 1499.88517 1499.85329 -0.00014 0.00002 -0.00004
in kB 1500.29745 1500.58586 1500.17384 -0.00009 0.00002 0.00000
in kB 1500.10129 1500.25323 1499.81734 0.00016 0.00004 0.00002
in kB 1500.08360 1500.17931 1499.73520 0.00020 0.00001 0.00001
in kB 1500.07581 1500.15166 1499.90178 0.00048 0.00001 -0.00001
in kB 1500.07394 1500.13570 1500.00074 0.00028 0.00001 0.00000

这个压力是正确的。

为什么做动力学的时候（IBRION = 0）压力显示为4000多？
多谢

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