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General DiscussionHi,

I'm wondering why BerkeleyGW can only use NCPP. I read from the BGW literature that "Note that norm-conserving pseudopotentials must be used, or else extra contributions would need to be added to our matrix elements." Could you please provide more reference explaining this? Thank you very much.

## Core Permalink

Submitted by jornada on Mon, 02/29/2016 - 16:26

The main idea is the following:

When you relax the norm-conservation condition, you are essentially approximating the true quasiparticle wave function |mk⟩ as a sum of two terms: the pseudo-wavefunction |m`k⟩, which is expressed in terms of plane-wave coefficient, and a correction term |Bk⟩ that is only "on" near the core region. So, you cannot express matrix elements such as ⟨mk| e^{-i(q+G)r} |nk+q⟩ solely in terms of the pseudo-wavefunction coefficients ⟨m`k| e^{-i(q+G)r} |n`k+q⟩, and you'll end up extra terms that depends on these set of |Bk⟩. We don't currently support the computation of these extra terms in BerkeleyGW.

A good reference for these extra matrix elements is Blochl's original work which introduced the Projected Augmented Method: http://journals.aps.org/prb/abstract/10.1103/PhysRevB.50.17953

Cheers,

Felipe

## ONCVPSP is very good Permalink

Submitted by babarker on Fri, 09/30/2016 - 12:34

Hello enixchen and BGW forum users,

While BerkeleyGW can not use wavefunctions generated from Vanderbilt pseudopotentials, the relatively new scheme by Prof. Hamann is pretty close to being a "best of both worlds" approach, requiring a reduced kinetic energy cutoff (compared to say, TM or RRKJ) while also conserving norms.

A good source of ONCVPSP files is listed at http://www.pseudo-dojo.org/ . (The usual caveats about manually verifying the quality of pseudopotentials applies.) The input parameters at pseudo-dojo appear to be very "stable" with respect to changes of various other input options, such as addition of further angular momentum channels, etc.

Best,

Bradford A. Barker