Inelastic neutron scattering, Raman, vibrational analysis with anharmonic corrections, and scaled quantum mechanical force field for polycrystalline l-alanine

Robert W. Williams, Sebastian Schlücker, Bruce S. Hudson

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)1-18
Number of pages18
JournalChemical Physics
Volume343
Issue number1
DOIs
StatePublished - Jan 22 2008

Keywords

  • Anharmonic corrections
  • Atomic displacement parameters
  • BOMD
  • Born-Oppenheimer molecular dynamics
  • Crystals
  • DFT
  • INS
  • Mean square displacements
  • Quantum mechanical force field
  • Raman neutron scattering
  • ZPE
  • density functional theory
  • inelastic neutron scattering
  • l-alanine
  • zero-point energy

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Fingerprint Dive into the research topics of 'Inelastic neutron scattering, Raman, vibrational analysis with anharmonic corrections, and scaled quantum mechanical force field for polycrystalline l-alanine'. Together they form a unique fingerprint.

Cite this