Towards the development of a quantum chemical diamond anvil cell

High-pressure chemistry investigates the effects of static isotropic compression on molecular systems, revealing phenomena such as novel bonding motifs, amorphization, altered reaction pathways, and pressure-induced changes in spectroscopic and structural properties. The Diamond Anvil Cell (DAC), capable of reaching pressures in the gigapascal range, has become a key tool for probing such effects. Alongside experimental advances, theoretical methods for modeling high-pressure phenomena are essential for interpreting results and guiding the discovery of new materials.
This thesis develops and applies computational methods to simulate high-pressure phenomena, with the aim of contributing to a theoretical toolbox for the understanding of DAC experiments. Three projects were undertaken:

- The optimization of the Gaussians on Surface Tesserae Simulate Hydrostatic Pressure (GOSTSHYP) code, resulting in an efficient integral screening procedure and memory reduction algorithms that enable large-scale simulations. Furthermore, the newly developed outer cavity correction allows for stable SCF convergence of GOSTSHYPcalculations.
- The derivation and implementation of the analytical Hessian for the extended Hydrostatic Force Field (X-HCFF) model, allowing for the prediction of pressure-induced vibrational shifts with good agreement to experimental Raman spectra.
- The development of a high-pressure conformational sampling workflow within the CREST program, which successfully reproduced qualitative features of high-pressure Raman spectra for a methane cluster and found conformational changes responsible for spectroscopic shifts in tetra(4-methoxyphenyl)ethylene.

Consequently, this thesis provides significant advancements in the applicability of the implicit pressure models X-HCFF and GOSTSHYP. The developed conformational sampling workflow shows strong potential for bridging a methodological gap between molecular dynamics and periodic DFT in modeling amorphous and solvated systems under pressure. These results represent significant progress toward a comprehensive theoretical DAC framework capable of accurate and efficient prediction of high-pressure phenomena.