Enhancing Molecular High-Pressure Simulations by Implicit Solvation.

Gaussians On Surface Tesserae Simulate HYdrostatic Pressure (GOSTSHYP) and the eXtended Hydrostatic Compression Force Field (X-HCFF) are quantum chemical methods to simulate the effects of pressure on a single molecule. Both methods have the usage of discretized molecular surfaces in common, which are also needed in implicit solvation models like the Conductor-like Polarizable Continuum Model (C-PCM). However, a combined usage of GOSTSHYP or X-HCFF with C-PCM was not possible in previous implementations inside the Q-Chem program package. To address this circumstance, we present an independent surface construction routine for both of the pressure models. This routine enables a stable combination of C-PCM with GOSTSHYP or X-HCFF, which serves as the first step to consider the chemical surrounding inside these two pressure models. For three different compounds occurring in both neutral and zwitterionic forms, the energetic difference between these states under pressure via GOSTSHYP was investigated. Especially for compounds occurring in both zwitterionic and neutral structures, the C-PCM is essential to access the zwitterionic state. Calculated pressure dependencies in the Raman spectra of the zwitterionic structure of glycine show good agreement with experimental data. The dimerization reaction of orthosilicic acid at elevated pressure is also influenced by implicit solvation, leading to better agreement between the simulations and the experimental data. This study paves the way for the inclusion of explicit solvation to disentangle intra- and intermolecular effects that cause geometric and spectroscopic changes under pressure applied with GOSTSHYP and X-HCFF.