Inquiry Regarding Second-Order Elastic Constants Calculation

[KylinGuo]

Dear MuST Development Team,

I hope this message finds you well.

I would like to inquire about the capability of MuST in calculating second-order elastic constants for alloys. Specifically, I have the following questions:

• Is there a tutorial or documentation available that can guide me through the process of calculating the second-order elastic constants of alloys using MuST?
• Does MuST have a built-in subroutine for calculating second-order elastic constants?
• From my experience with the VASP code, I am familiar with two common methods for calculating these constants: the energy-strain method and the stress-strain method. Do either of these methods (or similar alternatives) exist in MuST, or would I need to implement them manually?

Thank you for your time and assistance. I look forward to your response.

Best regards,
Qilin.

[vishnu2709]

Hi,

To the best of my knowledge, there is no in-built elastic constant calculation subroutines in MuST. But I've attached a couple of python programs that I wrote a few years ago that will calculate create displacements and use finite difference on the energies to calculate the full Cij matrix (assuming no symmetry)

https://gist.github.com/vishnu2709/cbbeca8ba55dd81b821ce66d16cc9be3

First, you need an input file, the base position file and the potentials you're going to use
Then run
python make-strains.py (strain) (name_of_input_file) (number_of_potentials)

For eg, If I'm doing a pure Cu calculation, my input file is called i_mst and I have one potential file Cu_mt_v, I would call
python make-strains.py 0.015 i_mst 1

(Using 0.015 as strain for finite difference is a thumb rule I use from experience, but generally it's a good idea to try a few values)

This will make (a lot of) folders containing all the strained systems, on which you can run MuST. Once all the calculations are done, the Cij matrix can be extracted using

python calCij.py (sysname_as_specified_in_MuST_input_file) (strain) (number_of_atoms)

For eg, python calCij.py Cu 0.015 4
This will put the Cij matrix in a file called Cij.dat

Note that because of no symmetry it will create displacements for all possible directions, if you want to do a cubic or other isotropic systems, you can modify the code to not create displacements for those modes.

Let us know if this works for you. Of course you are free to improve the scripts in any way you like

Regards,
Vishnu

[KylinGuo]

Vishnu

Hi, Vishnu! Thank you. I will try it.