[Wien] Doubts regarding the volume optimization of a triclinic cell

[Peter Blaha]

A full optimization of a bigger triclinic structure is hardly possible 
with WIEN2k.

It depends a lot on what the purpose of your calculations is, but:

a) Most importantly, optimize the position of the atoms using the 
forces:   run_lapw  -min ...

b)  eventually I'd next do a volume optimization (x optimize, option 1)
Do not forget the   -min switch in run_lapw, otherwise the results are 
nonsense. Volume changes give the largest change in E-tot.
Note, that other separate options of x optimize are rather useless for 
this purpose. One cannot optimize alpha,beta,gamma for fixed a,b,c. This 
is nonsense.

c) eventually you may use   optimize_abc_lapw -t 3 ...
This optimizes a,b,c independently but simultaneously. Again don't 
forget the -min switch.

For such a large cell, such calculations can be very time consuming when 
you do not use well adapted parameters (RKmax, k-points) and a good 
parallelization strategy on a sufficient number of cores.

Am 22.10.2021 um 04:54 schrieb Anupriya Nyayban:
> Dear users and experts,
> 
> I have a triclinic structure (P1 space group) with lattice parameters 
> a=18.508, b=39.835, c=40.199 Bohr; α = 119.701 ◦ , β = 103.309 ◦ , γ = 
> 90.0 ◦.  I have the following doubts
> 1) The volume obtained with these lattice parameters as well angles 
> (with the formula for triclinic cell) is not the same as the volume 
> (24823.466 Bohr^3) found in the scf file (VOL).
> 2) The mailing list suggests volume optimization by a) varying a, b, c 
> while α, β, γ are constant; b) varying α, β, γ with fixed a, b, c. I 
> have done volume optimization by varying volume with constant a:b:c. But 
> I am not able to find the suitable switch for the case b) in the 
> optimize.job script.
> Your valuable suggestion is highly appreciated!!
> 
> Thank you!!
> -- 
> With regards
> Anupriya Nyayban
> Ph.D. Scholar
> Department of Physics
> NIT Silchar
> 
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-- 
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
WWW:   http://www.imc.tuwien.ac.at
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