[Wien] abnormal behaviour in lattice parameters with applied pressure

[Fecher, Gerhard]

what do you "optimize" after you applied the pressure ?

You have the optimized lattice parameter, then you use the lattice parameter (volume) under pressure, and then you optimize it again
I would expect that you find always the same lattice parameter (within numerical noise),
what do you expect ?

Ciao
Gerhard

DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
"I think the problem, to be quite honest with you,
is that you have never actually known what the question is."

====================================
Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
and
Max Planck Institute for Chemical Physics of Solids
01187 Dresden
________________________________________
Von: Wien [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Dr. K. C. Bhamu [kcbhamu85 at gmail.com]
Gesendet: Dienstag, 27. Juni 2017 12:54
An: A Mailing list for WIEN2k users
Betreff: [Wien] abnormal behaviour in lattice parameters with applied pressure

Dear Prof. Peter and other Wien2k users

*The parent structure file for all below calculations was well-optimized one and then I performed two calculations with applied pressure.

I am trying to do pressure calculation of a ternary compound. I applied pressure from 0 to 14GPa in step of 2GPa. Without optimization, I see a clear decrease in the lattice parameters.
Unoptimised lattice parameters with mentioned pressure (in GPa).
0P  19.246483
2P  19.094359
4P  18.959055
6P  18.836998
8P  18.726089
10P  18.624460
12P  18.530711
14P  18.443746


But when I optimize the lattice parameters the lattice parameters first decrease up to 4P then increase up to 12P and then decrease for 14P.

0P      19.248
2P      19.2479
4P      19.245
6P      19.248
8P      19.2489
10P     19.2504
12P     19.251
14P     19.2507

So my queries are:

1. Please comment on this trend in lattice parameters.

2. In the case of 0P and 6P, the optimized lattice parameters are same which will give the same case.struct file. Obviously, the results for 0P and 6P would be same. I wonder if someone could give input on this situation. The applied pressure should change the properties.



Regards

Bhamu