[Pw_forum] a question about how to choose the best relaxed structure

[xu yuehua]

hi everyone here :
 i have a puzzled question about the relaxed structure :
i relaxed a structure : ,i set c direction of crystal lattice is 2.7950 and
the final result is

 entering subroutine stress ...

          total   stress  (Ry/bohr**3)                   (kbar)     P=   -
1.06
  -0.00000893  -0.00000001  -0.00000001         -1.31      0.00      0.00
  -0.00000001  -0.00000892   0.00000000          0.00     -1.31      0.00
  -0.00000001   0.00000000  -0.00000382          0.00      0.00     -0.56


     bfgs converged in  25 scf cycles and  22 bfgs steps

     End of BFGS Geometry Optimization

     Final energy =    -137.7926586085 Ry
so , i reduced the length of c ,set to 2.760, and the result is :

 entering subroutine stress ...

          total   stress  (Ry/bohr**3)                   (kbar)     P=   -
0.81
  -0.00000882  -0.00000004   0.00000001         -1.30     -0.01      0.00
  -0.00000004  -0.00000881   0.00000000         -0.01     -1.30      0.00
   0.00000001   0.00000000   0.00000106          0.00      0.00      0.16


     bfgs converged in  35 scf cycles and  32 bfgs steps

     End of BFGS Geometry Optimization

     Final energy =    -137.7921913584 Ry
and  my problem is which the structure is better ?
according to stress ,seems latter,but accrording  the energy ,seems the
 former ?
i do not know
so please give me some help
thank you



-- 
Xu Yuehua
physics Department of Nanjing university
China
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