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

[Gavin Abo]

I follow that your lattice parameters a=18.508 Bohr, b=39.835 Bohr, 
c=40.199 Bohr, α=119.701 degrees, β=103.309 degrees, and γ=90.0 degrees 
using the equation at [1] give you

Volume_triclinic = 18.508 Bohr*39.835 Bohr*40.199 
Bohr*sqrt(1-cos(119.701 degrees *(π radians/180 
degrees))^2-cos(103.309*(π radians/180 degrees))^2-cos(90.0*(π 
radians/180 degrees))^2+2*cos(119.701 degrees *(π radians/180 
degrees))*cos(103.309 degrees *(π radians/180 degrees))*cos(90.0 degrees 
*(π radians/180 degrees))) ≈ 24823 Bohr^3.

I also remember reading that the :VOL in case.scf is for the primitive 
unit cell [2-4].

Regarding the 20805.429 Bohr^3, I don't seem to be seeing enough 
information regarding that.  Thus, I'm unable to follow where you are 
getting that from.

I have seen the post at [5] describing how a triclinic optimization 
could be done.

However, in addition to that post I have read other posts about how it 
requires too many calculations for triclinic such that it not likely 
reasonably possible to do [6-8].

For example, say your advising professor says he needs a triclinic 
optimization one week from now.  However, say it takes 1 day to run and 
complete a single calculation on your initial triclinic structure.  Now, 
if you fixed b, c, α, β, γ and varied lattice constant a with four 
different values you would expect those calculations to take about 4 
days.  However, to fully optimize the structure you would also need to 
vary b, c, α, β, and γ as well such that you would need to do 4096 
calculations in total as explained in [5].

Thus, you could estimate that it would take 4096 days or about 11 years 
(=4096/365.25).  So it not possible to meet the professors deadline, but 
the calculation is possible but would take 11 years.  However, another 
problem with that could be that you run out of hard drive space and 
cannot afford the cost to buy more hard drives to store the data from 
all those 4096 calculations.

Furthermore, if you are like me, where I sometimes mess up my 
calculation setup during initialization (init_lapw).  I would probably 
check the result after 11 years to find out I setup the calculation 
wrong and have to start over.

So for me it would probably end up similar to the scenerio in The 
Hitchhiker's Guide to the Galaxy where my GIGO [9] mistake during 
initialization would end with a result like 42 [10].

[1] https://www.globalsino.com/EM/page3033.html
[2] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg20184.html
[3] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg14487.html
[4] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg19755.html
[5] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg10777.html
[6] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg01914.html
[7] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg10505.html
[8] 
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg21450.html
[9] https://en.wikipedia.org/wiki/Garbage_in,_garbage_out
[10] 
https://en.wikipedia.org/wiki/Phrases_from_The_Hitchhiker%27s_Guide_to_the_Galaxy#The_Answer_to_the_Ultimate_Question_of_Life,_the_Universe,_and_Everything_is_42

On 10/23/2021 1:18 AM, Anupriya Nyayban wrote:
> Dear Prof. Blaha and Dr. Bhamu,
>
> Thank you Prof. Blaha for the valuable suggestion and I have followed 
> all the steps as you have mentioned for the optimization. But still I 
> have doubt when I am going to calculate the optimized lattice 
> parameters from the optimized volume. The initial volume calculated 
> using the lattice parameters before the volume optimization (values I 
> have mentioned earlier) is 20805.429 Bohr^3. The scf file (before the 
> volume optimization) shows the lattice parameters (LATT) and volume 
> (infact this volume is the volume before inducing the mixing  into the 
> 2*2*2 supercell) to be "a=18.508, b=39.835, c=40.199 Bohr; α=119.701◦, 
> β=103.309◦, γ=90.0◦" and "24823.466 Bohr^3", respectively. I am 
> confused about the initial volume which one I should consider and why 
> is this dissimiarity?
>
>
> -- 
> With regards
> Anupriya Nyayban
> Ph.D. Scholar
> Department of Physics
> NIT Silchar
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