positive total energy

[IBRAHIM]

Dear All,

I obtained a positive total energy when using the Ag-sv-GW POTCAR for Ag system; however, this was not the case with the Ag-PBE and Ag-GW POTCARs.

Could you please check why this happened?

Many thanks in advance,
Ibrahim

[martin.schlipf]

I can confirm that the positive total energy exists. It is a bit larger than I would expect to see for these systems. However, absolute energies are meaningless with a pseudopotential method. The only important quantity are relative energies. To get these, I computed the bare atom by just removing the last three atoms from your structure. It turns out that this energy is also positive for the problematic POTCAR.

Code: Select all

POTCAR           energy-atom   energy-cluster   4*atom-cluster
--------------------------------------------------------------
PAW_PBE Ag       -0.03877022      -5.43378560       5.27870471
PAW_PBE Ag_GW    -0.03846161      -5.44581400       5.29196758
PAW_PBE Ag_sv_GW  2.02465203       2.80553583       5.29307220

So the energy differences are fine. The softer PAW has a bit larger difference but the two GW potentials yield more or less the same energy.

Btw, if you set all MAGMOM to 0 it is better to calculate with ISPIN=1. This leads to faster calculations and faster convergence.