Most of the programs use rectilinear normal coordinates in frequency calculations. The molecular vibrations defined by rectilinear normal coordinates are based on the infinitesimal approximation of the nuclear displacements. Therefore, such coordinates are not the useful for describing the molecular vibrations involving large displacements from the equilibrium. For such vibrations curvilinear coordinates system is best choice.
Let me know program that do vibrational calculations in curvilinear coordinates system?
There is program "shrink" by V.A. Sipachev.
[1]. Sipachev, V. A. Vibrational effects in diffraction and microwave experiments: A start on the problem / V. A. Sipachev // Advances in molecular structure research / Ed. I. Hargittai, M. Hargittai. / Ed. - New York: JAI Press, 1999. - Vol. 5 - P. 263.
[2]. Calculation of shrinkage corrections in harmonic approximation / V. A. Sipachev // J. Mol. Struct. (Theochem). - 1985. - Vol. 121. - P. 143-151.
See also an old paper:
@article{Dachsel1994,
abstract = "We develop the theoretical tools for a realistic visualization of curvilinear ..."
author = "Dachsel, H. and Sosna, D. and Quapp, W.",
doi = "10.1016/0166-1280(94)03769-H",
issn = "0166-1280",
journal = "Journal of Molecular Structure: \{THEOCHEM\}",
pages = "35--42",
title = "{An approach to a realistic visualization of curvilinear molecular vibrations}",
url = "http://www.sciencedirect.com/science/article/pii/016612809403769H",
volume = "315",
year = "1994"
}
Hi,
First of all, I am not sure to understand your request fully. You want to compute the vitrations using curvilinear coordinates... in what approximation ? If you use the harmonic approximation, then the vibration you will get won't be good far from equilibrium.
Any way, i would have thought of the following: 1) compute the normal mode using cartesian coordinate. 2) use these normal mode as curvilinear coordinates to sample things further from the equilibrium geometry.
Pulay has published something like this in the late 70s: if I remember correctly, he used the normal mode to perform anharmonic analyses.
Regards,
Paul.
The following paper may be of interest:
F. Jensen, D. S. Palmer " Harmonic Vibrational Analysis in Delocalized Internal Coordinates. " J. Chem. Theory Comp. 7 (2011) 223-230
- Badges
- Science topic