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slow_winds

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注册: 2013-12-11

[交流] VASP计算压电张量不对称

请教各位一下，在下刚刚转来用VASP做钙钛矿结构压电材料的第一性原理计算，但是现在计算中出现了一些问题，我计算P4mm的四方相结构时，压电离子贡献24与15方向不相等，导致计算出来的e24也不等于e15，请教下是什么原因。
POSCAR
KNbO3
1.00000000000000
   3.9780718153912340 0.0000000000000000 0.0000000000000000
   0.0000000000000000 3.9780718153912340 0.0000000000000000
   0.0000000000000000 0.0000000000000000 4.0697524641330913
K Nb O
1 1 3
Direct
  0.0000000000000000  0.0000000000000000  0.0208122828936224
  0.5000000000000000  0.5000000000000000  0.5370745926342191
  0.5000000000000000  0.5000000000000000  0.9956543127557665
  0.0000000000000000  0.5000000000000000  0.4982294058581956
  0.5000000000000000  0.0000000000000000  0.4982294058581956

INCAR
SYSTEM = KNbO3

  ISTART =  0
  ICHARG =  2
  PREC =  Accurate
  EDIFF  =  1E-06
  EDIFFG =  -0.005
  NSW =  1
  POTIM  =  0.2
  NFREE  =  2
  IBRION =  8
  LEPSILON = Ture
  ISIF =  3
  ISPIN  =  1
  NELM =  60
ISMEAR = 0
SIGMA  = 0.2
LREAL = Auto
LCHARGE = False
LWAVE = False

计算结果
PIEZOELECTRIC TENSOR  for field in x, y, z       (C/m^2)
      XX       YY       ZZ       XY       YZ       ZX
  --------------------------------------------------------------------------------
  x    0.00000    0.00000    0.00000    0.00000    0.00000    0.19952
  y    0.00000    0.00000    0.00000    0.00000    0.19957    0.00000
  z    0.16714    0.16714    0.06456    0.00000    0.00000    0.00000

PIEZOELECTRIC TENSOR IONIC CONTR  for field in x, y, z       (C/m^2)
      XX       YY       ZZ       XY       YZ       ZX
  --------------------------------------------------------------------------------
  x -0.00020    0.00055 -0.00176    0.00000    0.00000 -5.47889
  y -0.00076    0.00097 -0.00008    0.00000    1.73507    0.00000
  z -0.46524 -0.46524    4.83952    0.00000    0.00000    0.00000

d33值利用d=e*s计算出来只有20pC/N多点。烦请各位告知哪里有问题

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