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 >
