Theoretical Infrared Spectra: Quantitative Similarity Measures and Force Fields

Area of Science:

• Molecular spectroscopy
• Computational chemistry
• Chemical physics

Background:

• Infrared (IR) spectroscopy provides crucial data on molecular structure and dynamics.
• Extracting detailed information from IR spectra often necessitates theoretical calculations or simulations.
• Advancements in force fields include virtual sites, requiring adapted computational methods.

Purpose of the Study:

• To calculate and compare the infrared spectra of a large database of gas-phase compounds using multiple force fields.
• To assess the accuracy of modern force fields against experimental data and quantum chemical methods.
• To describe the implementation of normal-mode analysis for virtual site-containing molecules in GROMACS.

Main Methods:

• Normal-mode analysis was employed to compute IR spectra for 703 gas-phase compounds.
• Four distinct force fields were utilized: CGenFF, GAFF-BCC, GAFF-ESP, and OPLS.
• Pearson and Spearman correlation coefficients were applied to quantitatively compare calculated spectra with experimental data.

Main Results:

• The study calculated IR spectra for a database of 703 compounds using four force fields.
• The implementation of normal-mode analysis for virtual sites in GROMACS was detailed.
• Quantitative comparisons revealed that current force field methods do not achieve the accuracy of quantum chemical methods for IR spectra.

Conclusions:

• Force field-based calculations of IR spectra show limitations in accuracy compared to quantum chemical approaches.
• The evaluated force fields (CGenFF, GAFF-BCC, GAFF-ESP, OPLS) are insufficient for high-fidelity IR spectral prediction.
• Further development of force fields is needed to accurately model molecular vibrations and IR spectra.