DFT and QHA modelling of the thermodynamic properties of the molecular crystal of bromine

The input and output files describe calculation on solid bromine under pressure performed using Density Functional Theory (DFT) modelling, specifically the hybrid HSE06 functional with van der Waals corrections (Grimme-D3). All files are in ASCII format.

These calculations include geometry optimization, phonon dispersion, thermal properties and elastic constants, and were performed using the VASP code (versions 6.3.0 & 6.4.3).

Key computational parameters include a plane-wave basis set cut-off of 800 eV, SCF convergence criteria of 10^-8 eV, and a k-point mesh with a 2π × 0.033 Å⁻¹ spacing for structure optimization.

The directory structure is organized into three main folders.

1. Phonon : This folder contains eleven subfolders, each corresponding to a specific pressure (e.g., "0" for 0 GPa). Each subfolder contains two additional folders, ‘relax’ and ‘ph’, which contain necessary files for optimization and phonon calculations.

2. Thermal Properties & QHA : This folder contains an ‘e-v.dat’ file that contains energy and volume data for each pressure. It also includes ‘thermal_properties.yaml’ files, derived from phonon frequency calculations using the Phonopy code, which are used to generate thermal properties through the Quasi-Harmonic Approximation (QHA).

3. Mechanical Properties : This folder also contains eleven subfolders, each representing a different pressure. Each subfolder stores the required files for elastic tensor calculations.

 Description of the key files:

- POTCAR = PAW pseudopotential file for solid bromine

- INCAR = input parameters (pressure, energy cut-off, convergence parameter) for VASP calculation

- POSCAR and CONTCAR = lattice parameters and ionic positions of the optimized structures

- KPOINTS = k-point sampling

- IBZKPT = automatically generated k-mesh

- OSZICAR = a short summary of the SCF convergence step and energy

- *.vasp = optimized structure

- *.FORCE_SETS = [pressure in kbar] – force sets at a given pressure

- *.sh = scripts used for submitting the calculations to the queueing system

- ELASTIC_TENSOR = represents the elastic constants derived from the strain-stress relationship as obtained from the OUTCAR file.

- phonon.dat = file contains the phonon frequencies (in THz) across the Brillouin zone

- irreps_*.yaml = files display the irreducible representations of the phonon modes, along with their character tables