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Ab initio simulation of the IR spectra of pyrope, grossular, and andradite
Author(s) -
ZicovichWilson C. M.,
Torres F. J.,
Pascale F.,
Valenzano L.,
Orlando R.,
Dovesi R.
Publication year - 2008
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.20993
Subject(s) - pyrope , grossular , andradite , basis set , hamiltonian (control theory) , ab initio , chemistry , spectral line , wannier function , molecular physics , physics , computational chemistry , condensed matter physics , quantum mechanics , materials science , mineralogy , density functional theory , mathematics , mathematical optimization , quartz , skarn , fluid inclusions , composite material
IR spectra of pyrope Mg 3 Al 2 Si 3 O 12 , grossular Ca 3 Al 2 Si 3 O 12 and andradite Ca 3 Fe 2 Si 3 O 12 garnets were simulated with the periodic ab initio CRYSTAL code by adopting an all‐electron Gaussian‐type basis set and the B3LYP Hamiltonian. Two sets of 17 F 1 u Transverse Optical (TO) and Longitudinal Optical (LO) frequencies were generated, together with their intensities. Because the generation of LO modes requires knowledge of the high frequency dielectric constant ε ∞ and Born effective charges, they were preliminary evaluated by using a finite field saw‐tooth model and well localized Wannier functions, respectively. As a by‐product, the static dielectric constant ε 0 was also obtained. The agreement of the present calculated wavenumbers (i.e. peak positions) with the available experimental data is excellent, in that the mean absolute difference for the full set of data smaller than 8 cm −1 . Missing peaks in experimental spectra were found to correspond to modes with low calculated intensities. Correspondence between TO and LO modes was established on the basis of the overlap between the eigenvectors of the two sets and similarity of isotopic shifts; as result, the so called LO‐TO splitting could be determined. Animation of the normal modes was employed to support the proposed pairing. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008