[Pw_forum] stress and electric field (paolo umari)

[umari at democritos.it]

Dear Hanghui,

the present version of pw.x does not support yet the calculation
of stress in the presence of an electric field with ultrasoft 
pseudopotentials, but only with normconserving
pseudopotentials

> If I turn on a 'sawtooth' potential, the code explicitly warns that
> "Presently stress not available with electric field". However if I use the
> Berry phase method to turn on an electric field in the bulk, is the stress
> calculated correctly? If yes, then why we can calculate stress in the Berry
> phase method but not with the 'sawtooth' potential? If not, does that mean
> the stress is not meaningful in the Berry phase method?

the saw-tooth potential is meaningful only for isolated molecules or
slabs. However,  for isolated molecules or slabs  the notion of stress
becomes meaningless, so the correct way is to use the Berry's phase
method

Best regards,

Paolo Umari - Democritos

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