[Pw_forum] Res: vc-relax, GGA

Álvaro Alves asafis at yahoo.com.br
Tue Aug 24 19:44:09 CEST 2010

Hello, Guda. The  errors in the determination of lattice parameters (a, b, c, 
alpha, beta  and gamma) are 1.5%, 0.9%, 1.6%, 0.7%, 0.04% and 2.1%, 
respectively. But  the problem is that the value found for the alpha angle is 
slightly  lower than the experimental value despite being GGA functional. In 
this case, all or not should not be overestimated?


A. S. Santos

Univesidade Federal Fluminense
Niterói-Rio de Janeiro-Brasil 


De: Guda Karthik <karthik.guda at gmail.com>
Para: PWSCF Forum <pw_forum at pwscf.org>
Enviadas: Terça-feira, 24 de Agosto de 2010 13:57:17
Assunto: Re: [Pw_forum] vc-relax, GGA

GGA results tend to overestimate the lattice parameters where as LDA results 
tend to underestimate the lattice parameters. Check how much is the error% in 
your DFT calculations.


On Tue, Aug 24, 2010 at 12:35 PM, Álvaro Alves <asafis at yahoo.com.br> wrote:

Hello PWscf users. I optimize a triclinic cell using the vc-relax, GGA 
functional. My expectation was that all values of the calculated parameters were 
slightly higher than the respective experimental values. But, the angle alpha 
showed a value slightly lower. The experimental value is in degree, 103.32, the 
calculated value is 102.6. There is some inconsistency in this result?
>A. S. Santos
>Univesidade Federal Fluminense
>Niterói-Rio de Janeiro-Brasil 
>Pw_forum mailing list
>Pw_forum at pwscf.org

Karthik Guda
Graduate Student
Materials Engineering
Purdue University

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