This package is based on python to create deformed structure and calculate second-order elastic constants from strain-energy relationship. This tool is only compatible with DFT package VASP.

Kindly cite following articles if you find this package useful.

1. Kumar, P., and Adlakha, I. (July 26, 2022). "Effect of Interstitial Hydrogen on Elastic Behavior of Metals: an Ab-Initio Study." ASME. J. Eng. Mater. Technol. doi: https://doi.org/10.1115/1.4055097

@article{Elastic_vasp,
    author = {Kumar, P. and Adlakha, I.},
    title = "{Effect of Interstitial Hydrogen on Elastic Behavior of Metals: An Ab-Initio Study}",
    journal = {Journal of Engineering Materials and Technology},
    volume = {145},
    number = {1},
    year = {2022},
    month = {08},
    issn = {0094-4289},
    doi = {10.1115/1.4055097},
}

Installation

pip install elastic-vasp

How to use this Package

The repository now keeps the original code line on the legacy branch and the current refactored code on main.

Preprocessing

from elastic_vasp import elastic_gen as eg

eg.cubic_pre()

The above code for cubic elastic constants creates three folders: C11_C12_I, C11_C12_II, and C44. Each folder contains one subfolder per strain value from strain.dat. Zero strain is normalized automatically, so 0, 0.0, and 0.00 all work.

Inside each strain folder, a new POSCAR is created for the deformed structure. After preprocessing, copy KPOINTS, POTCAR, and INCAR into every strain folder. You can use the bundled copy.sh script to automate that step.

After the VASP calculations finish, run post-processing to print the elastic constants.

Post Processing
you can run post processing command to print elastic constants

from elastic_vasp import constants 

C = constants.cubic_post()

Available post-processing functions:

cubic_post()
hexagonal_post()
orthogonal_post()
trigonal_1_post()
trigonal_2_post()
monoclinic_post()
triclinic_post()

Available preprocessing functions:

cubic_pre()
orthogonal_pre() ------ for orthorhombic and Tetragonal
hexagonal_pre() 
trigonal_1_pre()
trigonal_2_pre()
monoclinic_pre()
triclinic_pre()

Things to keep in mind:

1. Use direct coordinate in initial POSCAR
2. Use ISIF=2 only for calculation
3. You should know the symmetry of the crystal before preprocessing. Use the example folders for tests. To determine symmetry, use spglib or phonopy.
4. Post-processing auto-detects the zero-strain folder from the strain_* names, so it no longer depends on strain_0.00 specifically.

Crystal system	Space-group	No. of independent elastic constants
Triclinic	1-2	21
Monoclinic	3-15	13
Orthorhombic	16-74	9
Tetragonal I	89-142	6
Tetragonal II	75-88	7
Trigonal I	149-167	6
Trigonal II	143-148	7
Hexagonal	168-194	5
Cubic	195-230	3

For tetragonal systems, it is usually simpler to calculate orthorhombic elastic constants first. That avoids confusion about which axis is longer and lets you compute all 9 elastic constants directly.

Similarly, for trigonal systems, calculate all 7 elastic constants.

For any contact, visit my homepage
https://sites.google.com/view/prnvkmr4