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didi5158金蟲 (小有名氣)
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【求助】優(yōu)化的結果,scf計算該結構,force為什么仍然很大? 已有7人參與
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vc-relax計算晶體的晶格常數(shù),用計算所得到的結構再進行自洽計算,而所得結果中force,stress,total energy都差別較大,這個是為什么?請大家指教。 vc-relax計算結果: --------------------------------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------------------------------- 用上面所得到結構,scf計算結果: ---------------------------------------------------------------------------------------------------------- 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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| One possibility is that a fixed set of G-vector is selected using the initial cell based on the specified `ecutwfc`. This G-vector set is kept fixed during a vc-relax run (which can modify effectively the stored G-vectors through changes in the unit cell). As such, at the end of vc-relax, the planewave cutoff can differ from direct scf calculation if the unit cell undergoes sizable strain. One solution to this problem is to use the approach by M. Bernasconi et al, [J. Phys. Chem. Solids 56, 501 (1995), doi:10.1016/0022-3697(94)00228-2]. Relevant QE input parameters include: ecfixed, qcutz, and q2sigma see: https://www.quantum-espresso.org/Doc/INPUT_PW.html#idm406 |
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