[Pw_forum] question on potential energy in constant pressure simulations

Konstantin Kudin konstantin_kudin at yahoo.com
Thu Apr 20 17:36:30 CEST 2006

 Hi all,

 I am doing the CP dynamics with one of the lattice vectors being
optimized as well.

 I am using a very recent CVS (yesterday's), which should have the
correct stress (knocking on wood).

 The parameters for the modified kinetic energy functional are:
ecutwfc = 30.0, ecfixed = 25.0, qcutz = 25.0, q2sigma = 3.0
 This is for what used to be just ecutwfc=25.0 in constant volume

 So what I am seeing is that while the stress becomes smaller, the
potential energy of the system goes up at the same time with the
decreasing stress.

 Should not the decrease in stress correspond to the *decreasing*
potential energy? Or is there some funny business with this modified
kinetic energy functional such that I should disregard the potential
energy values and trust the stress instead ?


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