Virtually nonexistent correlation between the OH stretching frequency and the instantaneous geometry in the short...

We examined the correlation between the dynamically sampled anharmonic frequency of the OH stretching motion and the corresponding instantaneous geometric parameters associated with the structure of crystalline sodium hydrogen bis(sulfate), which is a benchmark system with an extremely short hydrogen bond. We analyzed the trajectory obtained by a conventional Car-Parrinello molecular dynamics simulation, followed by an a posteriori quantization of the proton motion. For statistical analysis we applied the established methodologies of multiple linear regression, principal component analysis, principal component regression, and Kohonen neural networks. No simple correlation scheme between the OH stretching frequency and any particular geometry parameter (or their combination) was found. In comparison to the established correlation schemes (e.g., Mikenda and Novak) that consider a series of systems, our study provides a complementary insight into the nature of hydrogen bonding of a single system, in the sense that it considers the important aspects of fluctuations of the environment and the resulting broadening of the OH stretching band, which cannot be adequately assessed by experiment. The absence of appreciable correlations gives strong evidence of the extreme complexity of short hydrogen bonding.