[QE-users] Difference between pw.x and cp.x for relax, ve-relax calculation

[Giuseppe Mattioli]

Dear Kejiang
As a very general rule, partially depending on the history of the  
codes included in the QE distribution, pw.x is the "engine" for  
electronic structure calculations (including geometry and cell  
optimizations, but also Born-Oppenheimer MD simulations), and cp.x the  
"engine" for Car-Parrinello ab initio molecular dynamics simulations.  
A very high degree of interoperability between the two codes has been  
achieved in more recent years, but as a useful rule of thumb it is  
still sensible to perform your calculations using the designated code.

Regarding the main parameters, of course using the same  
pseudopotentials with the same ecutwfc and ecutrho is a good starting  
point, but there are tips and tricks that depend on your actual setup.
HTH
Giuseppe

Quoting likejiang at ustb.edu.cn:

> Dear QE-Users,
>
> In QE 7.0, I noticed that the calculation choice for cp.x can also be
> 'relax', 'vc-relax', 'scf', and 'nscf' which are the key functions of pw.x.
> But the other parameters in cp.x are far less than the pw.x, for instance,
> it is known that K point cannot be set in cp.x.
>
> Could anyone help to explain the difference between pw.x and cp.x for
> 'relax', 've-relax' calculation.
>
> Because I am trying to do some CPMD simulation which can only be done with
> cp.x, I hope to use cp.x for 'relax' and 'vc-relax' calculation to keep the
> consistence of parameters in the whole process.
>
> Any comments or suggestions will be much appreciated.
>
> All the best,
> Kejiang
>
> -------------------------------------------------
> Dr. Kejiang Li
> School of Metallurgical and Ecological Engineering,
> University of Science and Technology Beijing
> Xueyuan Rd., Haidian District, Beijing 100083, P. R. China
> https://kejiangli.com/



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.mattioli at ism.cnr.it>