SS_2D_Materials

Python class designed to automatically identify and measure Spin Splitting (SS) effects in 2D materials, from DFT band structure calculations performed with VASP. It relies heavily on tools and functionalities implemented in Pymatgen and the Atomic Simulation Environment (ASE) python libraries.

Requirements / Premises:

The code was designed to work with output files from non-collinear band structure DFT calculations performed with VASP for 2D materials. It follows the following premises:

• The calculation correspond to a compound with a finite electronic band gap: metallic materials are currently not supported by the algorithm.
• The monolayer is disposed in the $xy$ plane of the unit cell: the algorithm forces periodic boundary conditions only in these directions, necessary for the correct description of the first Brillouin Zone for each system.
• The path in the reciprocal space employed in the band structure calculation was generated with ASE's Brillouin sampling automatic scheme

Usage

The code initialization requires only the specification of the folder path where the band structure calculation was performed:

from SS_2D_Materials.SSEntry import SSEntry

entry = SSEntry('path/to/calculation/folder')

Implemented methods:

• select_spin_splittings(): Main method for identifying and measuring SS effects in the material valance and conduction bands. It returns a nested dictionary it the keys corresponding to the the different proposed SS Prototypes, namely Linear Rashba/Dresselhaus SS (LSS), Zeeman SS (ZSS) and High-Order SS (HOSS). Inside each dictionary key, a list of dictionaries is presented with each one corresponding to a single identified SS, following are the main SS properties computed and available inside each dictionary:

  • label: High-symmetry k-point label.
  • direction: Direction of the k-path segment analyzed by the algorithm in the vicinity of the high-symmetry k-point.
  • rashba_param: Measured Rashba coefficient.
  • spin_splitting: Measured SS magnitude.
  • accessibility: Energy difference from the SS to the VBM/CBM of its corresponding band.
  • anti_crossing: Presence of anti-crossing bands among aligned SS across valance and conduction bands.

• band_structure_plot(): Method for quickly plotting the materials band structure, based on the eigenvalues parsed by Pymatgen.

• spin_plot(): Method for plotting the materials band structure with spin texture resolution according to a specified projection axis, based on the values parsed from the PROCAR VASP output file.

• get_max_raw_ss(): Method for computing the maximum value for the SS magnitude in the materials valance and conduction bands.