[Pw_forum] how to read lattice constant from the output file of vc-relax

[Paolo Giannozzi]

On Saturday 27 August 2005 18:12, sun jason wrote:

> I execute a vc-relax calculation, the output file is like this:
> [...[
> does it mean that the lattice constant is changed to
> (0.500982241/0.5)*3.615=3.6221 angstrom? if it is right, the 
> lattice constant optimized by GGA pseudopotential using pwscf 
> code is large than the experimental value, but the GGA result 
> by CASTEP code is small than the experimental value. which 
> one is reasonable? 

variable-cell calculations locate the lattice constant at which 
the pressure vanishes. This method is typically much slower 
to converge wrt the kinetic energy cutoff than the good old 
method of fitting the E(V) curve to an equation of state.

GGA lattice parameters are often slightly larger than the
experimental results. In any event, if you compare calculations
performed under the same assumptions, you should find only 
minor differences between pwscf and castep.

Paolo

-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
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