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didi5158

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专业: 无机材料化学

[交流] 【求助】优化的结果，scf计算该结构，force为什么仍然很大？已有7人参与

vc-relax计算晶体的晶格常数，用计算所得到的结构再进行自洽计算，而所得结果中force，stress，total energy都差别较大，这个是为什么？请大家指教。

vc-relax计算结果：
---------------------------------------------------------------------------------------------------------
total energy             = -588.70418379 Ry
Harris-Foulkes estimate = -588.70418379 Ry
estimated scf accuracy <       3.9E-10 Ry

Total force =    0.000201    Total SCF correction =    0.000059
SCF correction compared to forces is too large, reduce conv_thr

entering subroutine stress ...
      total stress  (Ry/bohr**3)                (kbar)    P= 0.06
0.00000076 0.00000000 0.00000000       0.11    0.00    0.00
0.00000000 0.00000076 0.00000000       0.00    0.11    0.00
0.00000000 0.00000000  -0.00000024       0.00    0.00    -0.03

bfgs converged in  14 scf cycles and  12 bfgs steps
End of BFGS Geometry Optimization

Final enthalpy = -588.7041837859 Ry
new unit-cell volume = 657.99457 a.u.^3 ( 97.50473 Ang^3 )

CELL_PARAMETERS (alat)
0.781116722 0.000000000 0.000000000
  -0.390558361 0.676466924 0.000000000
0.000000000 0.000000000 1.486696131

ATOMIC_POSITIONS (crystal)
Li    0.333333333 0.666666667 0.250000000
Li    -0.333333333  -0.666666667  -0.250000000
F       0.420499391  -0.010919477 0.122948838
F       0.010919477 0.431418866 0.122948838
F    -0.431418866  -0.420499390 0.122948838
F       0.010919477  -0.420499390 0.377051161
F    -0.431418866  -0.010919477 0.377051161
F       0.420499390 0.431418866 0.377051161
F    -0.420499390 0.010919478  -0.122948838
F    -0.010919477  -0.431418866  -0.122948838
F       0.431418866 0.420499390  -0.122948838
F    -0.010919477 0.420499390 0.622948838
F       0.431418866 0.010919477 0.622948838
F    -0.420499390  -0.431418866 0.622948838
Al    0.666666667 0.333333333 0.250000000
Al    -0.666666667  -0.333333333  -0.250000000
Ca    0.000000000 0.000000000 0.000000000
Ca    0.000000000 0.000000000 0.500000000

----------------------------------------------------------------------------------------------------------

用上面所得到结构，scf计算结果：

----------------------------------------------------------------------------------------------------------
total energy             = -571.49242692 Ry
Harris-Foulkes estimate = -571.49242692 Ry
estimated scf accuracy <       2.4E-11 Ry

Total force =    0.262955    Total SCF correction =    0.000025

entering subroutine stress ...

      total stress  (Ry/bohr**3)                (kbar)    P=-4722.80
  -0.03210576 0.00000000 0.00000000    -4722.92    0.00    0.00
0.00000000  -0.03210576 0.00000000       0.00  -4722.92    0.00
0.00000000 0.00000000  -0.03210340       0.00    0.00  -4722.57
----------------------------------------------------------------------------------------------------------

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