[Wien] Pressure vs volume

[Andrei Postnikov]

On Thu, 25 Sep 2003, Neerja wrote:

| Dear All,
| I got method for calcualting bulk modulus for any crystal structure.
|
| Thanks a Lot....
|
| Now problem is that using eosfit, we can calcualte bulk modulus, but...we
| want to calculate pressure corresponding to any density for example if
| ground state density is rho_0 and we want to calculate pressure for
| 1.1rho_0, 1.2rho_0 ......2.0rho_0, than for crystal structures (other tahn
| cubic)..what can we do..........using WIEN2k.

Dear Neerja,

Using WIEN2k, you can fix the volume, MAKE FULL RELAXATION
(C/A and internal coordinates), get total energy.
Repeat this for a number of volumes, fit to the equation of state
and get pressure as function of volume, bulk modulus, whatever.
Mind that the relaxation of C/A and internal coordinates,
if they are free to change by symmetry, is important;
otherwise your Energy/Volume curve and hence bulk modulud will be wrong.

Another option, available in Siesta and certainly in a number of
planewave codes, is to set your target pressure and make
full relaxation (of volume, C/A, internal coordinates) to this
target pressure, using, e.g. the Parrinello-Rahman scheme.
This is not yet implemented in WIEN.

Good luck,

Andrei Postnikov

 +-- Dr. habil. Andrei Postnikov ----- Tel. +49-541-969.2377 -- Fax .2351 ---+
 | Universitaet Osnabrueck - Fachbereich Physik, D-49069 Osnabrueck, Germany |
 +-- apostnik at uos.de --------- http://www.home.uni-osnabrueck.de/apostnik/ --+