[Pw_forum] Mg.pz-n-vbc.UPF O.pz-mt.UPF give negative pressure in MgO md calculation

[Nicola Marzari]

Dear Lawrence,


1) please use your affiliation/address in these requests, if you'd like
people like me to answer them (you do not have to, but also I do not
have to answer)

2) the pressure will be zero at the equilibrium lattice parameter -
so please tell us which are the equilibrium lattice parameters of your
LDA and PW91 calculations, and how they differ from what is published in
the literature.

3) calculate the eq. lattice parameters in these two ways:

3a) minimize the energy as a function of lattice parameter
3b) find the volume at which the trace of the stress tensor is zero

3a) and 3b) should give the same results, provided you use a large
enough cutoff,  but 3a will converge faster with respect to the cutoff

4) do not post until you have the results for 3a and 3b.

Thanks,

				nicola

Lawrence Lee wrote:
> Dear all,
> 
> The pressure calculated by using the pseudo-potential (Mg.pz-n-vbc.UPF) 
> and (O.pz-mt.UPF) is negative! These two pp were downloaded from 
> www.pwscf.org.

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Prof Nicola Marzari   Department of Materials Science and Engineering
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