Ab Initio Molecular Dynamics Computation of the Infrared Spectrum of Aqueous Uracil

Abstract

Recent progress in the development of ab initio molecular dynamics methods for the computation of infrared absorption spectra in condensed molecular systems is reviewed and illustrated by a detailed account of an application to aqueous uracil. Similar to classical force field simulations, the spectrum is obtained as the Fourier transform of the polarization time autocorrelation function. The density functional methodology for the computation of electronic polarization in periodic supercells is briefly outlined, and also the effect of quantum corrections is discussed. The spectral patterns obtained for the model system in the 2000−1000 cm -1 domain are in good agreement with experiment. Comparing to the low-temperature vacuum spectrum computed by similar time-dependent methods, we found that the narrow amide bending band in a vacuum is spread out over a 500 cm -1 wide interval in solution with a substantially blue-shifted high-frequency end. The highest increase in frequency was found for N1−H1 bending. The red shift and broadening of C O stretching bands is, in comparison, a much smaller effect.