RepOD

EXP folder:

Results from Raman scattering measurements performed in diamond anvil cells. Raman spectra were obtained at room temperature using an Alpha300M+ confocal microscope (Witec Gmbh). A 532 nm laser line was delivered to the microscope via a single-mode optical fiber, with the laser power at the sample not exceeding 30 mW. The Raman signal was collected through a 50× long working distance objective (NA = 0.40) and transmitted through a photonic-crystal fiber to a lens-based spectrometer (Witec UHTS 300, f/4 aperture, focal length 300 mm) equipped with a back-illuminated Andor iDUS 401 detector, which was thermoelectrically cooled to -60 °C. The spectra were acquired using a 1800 mm grating, resulting in a spectral resolution of 1.2 cm^-1. The typical acquisition times ranged from 5 to 20 seconds with 15 to 30 accumulations. Additional area scans (120 µm x 120 µm in 2 µm steps) were performed at selected pressures using a 900 mm^–1 grating (spectral resolution of 5 cm^–1) in order validate sample homogeneity and pressure gradients within the DAC. The collected spectra were post-processed using the Project FIVE software (Witec Gmbh) be performing background subtraction, cosmic-ray removal, and smoothing. The positions of Raman bands were determined using the Fityk 1.3.1 software by fitting the observed bands with pseudo-Voigt profiles.

Description of files:

spectra.dat – normalized spectra obtained upon compression (Raman shift in cm^–1 in first column, pressure given in the header of each column

freq.dat – position of Raman bands (in cm^–1) obtained by fitting the Raman spectrum with with pseudo-Voigt profiles (pressure in GPa in first column)

DFT folder:

Input files and results of Density Functional Theory (DFT) modelling (geometry optimization and Raman spectrum calculations) performed in VASP 6.3.0 code for Mg₂SiO₄, Mg₂GeO₄, and Na₂CuF₄ (results for each compound in separate folders, each structure type in separate subfolder). Calculations performed using the DFT+U method at ambient and high pressure (each pressure step for a given stoichiometry and structure in separate subfolder). Force-sets used for vibrational properties calculations contained in separate subfolder.

Calculation parameters: 800 eV cutoff of the plane-wave basis set; PAW pseudopotentials; SCF convergence: 10^–7 eV per atom; k-point mesh with a 2π × 0.03Å⁻¹ spacing.

Description of selected files:

POTCAR – PAW pseudopotential file

*.vasp – optimized structures

INCAR – calculation parameters

KPOINTS – k-point sampling

OSZICAR – ionic and SCF convergence