[Pw_forum] Is Electronic-Enthalpy Functional for Finite Systems Under Pressure implemented in espresso-3.2?

[Hongjun Xiang]

Dear Dr. Cococcioni and others,
I tried some test calculations and realized that the pressure changes 
the electronic structure and thus
decreases the volume of the system. If I am interested in the band gap 
of a finite system under pressure, which method of the followings is 
correct?
(1) Relax the structure under the pressure, and calculate the gap using 
the relaxed structure under the pressure.
(2) Relax the structure under the pressure, and calculate the gap using 
the relaxed structure without the pressure.

It turns out the results from the above procedures are different.

Thank you very much.

Best regards,
Hongjun Xiang

=============================================================
H. J. Xiang
Postdoctoral Research Associate
National Renewable Energy Laboratory
http://www4.ncsu.edu/~hxiang/
============================================================= 


Matteo Cococcioni wrote:
>
> Dear Hongjun,
>
> the electronic enthalpy is not contained in the current official 
> version of the code (v 3.2).
> However it's implemented in the CVS version (README.cvs for 
> instruction on how to download it) of
> the package. Precisely it's contained in the CP part (directory CPV). 
> Instructions contained in
> INPUT_CP should be enough to run a calculation with the electronic 
> enthalpy. Otherwise feel free to ask for more help.
>
> Regards,
>
> Matteo
>