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计算弹性常数时INCAR如下:
SYSTEM=SiP
ENCUT=650
ISYM=0
ISTART=0;ICHARG=2
ISMEAR=0;SIGMA=0.1
ISIF=3
IBRION=6
NFREE=4
NSW=1
EDIFF=1E-6
EDIFFG=-0.01
#NPAR=8
LWAVE=FALSE
LCHG=FALSE
IVDW=1
LVDW=.TRUE.
IALGO=48
NELMIN=4
POTIM=0.1
计算过程报警如下:
VERY BAD NEWS! internal error in subroutine IBZKPT:
Reciprocal lattice and k-lattice belong to different class of lattices. Often results are still useful... 168
解决办法:
The message does not mean an
error.
The procedure
doing the evaluation of symmetry uses a numerical criterion
(SYMPREC=1E-5)
to determine
which atoms are symmetrically equivalent. When this criterion is too
soft
the programm
can find "false" symmetry and reports that "reciprocal lattice and k-lattice
belong
to different
class of lattices." To get rid of this message you can:
1) Switch off the symmetry
(ISYM=0)
2) Make the
treshold for detecting the symmetry more severe (SYMPREC=1E-8)
注:系统有一定的对称性但不太好,但程序的判定条件较低 (SYMPREC=1E-5,缺省?)而认为有对称,
如果设置上面两项,则需要的k点增多!
在INCAR中添加了SYMPREC=1E-8问题得到解决。
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