Inelastic neutron scattering,Raman, vibrational analysis with anharmonic corrections,and scaled quantum mechanical force field for polycrystalline l-alanine |
| |
Authors: | Robert W. Williams,Sebastian Schlü cker,Bruce S. Hudson |
| |
Affiliation: | 1. Department of Biomedical Informatics, Uniformed Services University, 4301 Jones Bridge Road, Bethesda, MD 20815, United States;2. Institute of Physical Chemistry, University of Würzburg, Würzburg, Germany;3. Department of Chemistry, Syracuse University, Syracuse, NY, United States |
| |
Abstract: | A scaled quantum mechanical harmonic force field (SQMFF) corrected for anharmonicity is obtained for the 23 K l-alanine crystal structure using van der Waals corrected periodic boundary condition density functional theory (DFT) calculations with the PBE functional. Scale factors are obtained with comparisons to inelastic neutron scattering (INS), Raman, and FT-IR spectra of polycrystalline l-alanine at 15–23 K. Calculated frequencies for all 153 normal modes differ from observed frequencies with a standard deviation of 6 wavenumbers. Non-bonded external k = 0 lattice modes are included, but assignments to these modes are presently ambiguous. The extension of SQMFF methodology to lattice modes is new, as are the procedures used here for providing corrections for anharmonicity and van der Waals interactions in DFT calculations on crystals. First principles Born–Oppenheimer molecular dynamics (BOMD) calculations are performed on the l-alanine crystal structure at a series of classical temperatures ranging from 23 K to 600 K. Corrections for zero-point energy (ZPE) are estimated by finding the classical temperature that reproduces the mean square displacements (MSDs) measured from the diffraction data at 23 K. External k = 0 lattice motions are weakly coupled to bonded internal modes. |
| |
Keywords: | INS, inelastic neutron scattering Raman neutron scattering l-alanine Crystals Quantum mechanical force field DFT, density functional theory Anharmonic corrections BOMD, Born&ndash Oppenheimer molecular dynamics ZPE, zero-point energy Atomic displacement parameters Mean square displacements |
本文献已被 ScienceDirect 等数据库收录! |
|