[Wien] optimization of an orthorhombic cell
Dr. K. C. Bhamu
kcbhamu85 at gmail.com
Sat Oct 14 21:18:31 CEST 2017
Dear Prof. Gerhard and Stefaan,
As the system is complex so to save my wall time, I need a confirmation
what I am following.
In a fresh calculation, after a structure relaxation, I have done C/A
optimization [VARY C/A RATIO with CONSTANT VOLUME and B/A (orthorh
lattice)].
The new optimization values are given below. It gives
Minimum value of C/A is = 0.983596
so this means that (C/A)_new =983596 (say "X")
C_new=(X)*(A_new). #A_new is taken from below set of data.
Should I go this way or A should be the old one?
Now update this C_new in struct file and then go for B/A optimization.
followed by volume optimization to get optimised A.
Minimum value of C/A is = 0.983596 >>>
minmum value of C/A
Minimum value of ENE is = -339059.101281 Ry
==========================================================
Value of A is = 14.66061 bohr ; 7.75806
Ang >> A_new
Value of B is = 21.69275 bohr ; 11.47931 Ang
Value of C is = 14.42012 bohr ; 7.63080 Ang
==========================================================
Initial value of C/A is = 0.973598
Conv. Unit Cell Vol = 4586.0140 bohr^3 ; 679.5773 Ang^3
==========================================================
Regards
Bhamu
On Fri, Oct 13, 2017 at 5:40 PM, Stefaan Cottenier <
Stefaan.Cottenier at ugent.be> wrote:
> No, not really. You have three (unit cell) degrees of freedom: E(a,b,c).
> Or similarly E(V, b/a, c/a) (with V=a*b*c). The different options in
> optimize_lapw give you a series of unit cells with either different values
> of V (and b/a and c/a constant), different values of b/a (and V and c/a
> constant) and different values of c/a (and V and b/a constant). These are
> three slices through the energy landscape. By finding the energy minimum
> along one slice, fix it, then go on with the next slice, etc. … you can
> gradually approach the absolute energy minimum. It might take several
> iterations through this scheme if your starting cell is far away from the
> minimum. Best is to start first with the degree of freedom that affects
> energy most (usually the volume).
>
>
>
> Stefaan
>
>
>
>
>
> *Van:* Wien [mailto:wien-bounces at zeus.theochem.tuwien.ac.at] *Namens *Dr.
> K. C. Bhamu
> *Verzonden:* vrijdag 13 oktober 2017 14:04
> *Aan:* A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.at>
> *Onderwerp:* Re: [Wien] optimization of an orthorhombic cell
>
>
>
> Thank you very much for a hint.
>
> I thought the value obtained from "VARY C/A RATIO with CONSTANT VOLUME and
> B/A (orthorh lattice)" are well optimised then why I do need to optimise
> all of them again.
>
> Now I see, B/A scaling will give us optimised b, then C/A scaling will
> give us optimised C and finally optimised v(=a*b*c) will give us optimised
> "a".
>
> Using optimised a,b,c structure relaxation will be done.
>
>
>
>
>
> I should be fine to optimised an orthorhombic cell. Is it?
>
>
>
>
>
>
>
>
> Regards
>
> Bhamu
>
>
>
> On Fri, Oct 13, 2017 at 11:18 AM, Fecher, Gerhard <fecher at uni-mainz.de>
> wrote:
>
> you have three quantities V=a*b*c, b=a*(b/a) and c=a*(c/a)
> so what is the problem ?
>
> 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: Freitag, 13. Oktober 2017 00:42
> An: A Mailing list for WIEN2k users
> Betreff: Re: [Wien] optimization of an orthorhombic cell
>
> Dear List,
>
>
> Could you please help me to get optimize lattice parameters from the
> procedure that I followed as mentioned below:
>
>
>
> The procedure is a four-step task what I am following:
>
> The original lattice parameters were: a, b, c=16.763005, 24.803600,
> 16.320431 >> vol 6785.64777697697 bohr^3.
>
>
> 1. VARY C/A RATIO with CONSTANT VOLUME and B/A (orthorh lattice)
>
> getting below optimized data:
> ==========================================================
> Lowest point on X-axis is = -1.615800
> Minimum value of B/A is = 1.455755
> Minimum value of ENE is = -339059.104498 Ry
> ==========================================================
> Value of A is = 16.85428 bohr ; 8.91890 Ang
> Value of B is = 24.53569 bohr ; 12.98373 Ang
> Value of C is = 16.40929 bohr ; 8.68342 Ang
> ==========================================================
> Initial value of B/A is = 1.479663
> Conv. Unit Cell Vol = 6785.7557 bohr^3 ; **********Ang^
>
>
> 2. Volume optimization using option 1 in "x optimize" and then
> calculating new volume from eplot option.
>
>
> Query: Step two is giving optimized volume but I do not know how to
> calculate lattices parameters from a single volume
> value for the next step "VARY C/A RATIO with CONSTANT VOLUME and B/A
> (orthorh lattice)"?
>
>
> The original cell volume and lattice parameters are mentioned at the
> beginning.
>
> and the new volume from step two is: 6815.3427 bohr^3
>
>
>
> The above same query is for the remaining process:
>
> 3. optimization of C/A
>
> 4. optimization of V.
>
>
> *5 At the final step I will do structural relaxation (min_.....).
>
>
> Could you please advice me how to proceed?
>
>
>
> Kind regards,
> Bhamu
>
>
>
>
>
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