[Pw_forum] a question about how to choose the best relaxed structure
Sandro Scandolo
scandolo at ictp.it
Sat Nov 24 15:18:49 CET 2007
Dear Xu Yuehua,
the calculated stress tensor is not exactly equal to the derivative of
the energy if the basis set is not complete. For a detailed discussion
see: http://www.quantum-espresso.org/wiki/index.php/Stress_calculations
Regards,
Sandro
xu yuehua wrote:
> 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
> ------------------------------------------------------------------------
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
More information about the Pw_forum
mailing list