@article { ISI:000284738900039,
	title = {On the Mean Accuracy of the Separable VSCF Approximation for Large Molecules},
	journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
	volume = {114},
	year = {2010},
	month = {DEC 9},
	pages = {20603-20608},
	abstract = {The separable VSCF approximation and the VSCF-PT2 method are extensively used for anharmonic vibrational spectroscopy calculations of large molecules. VSCF-PT2 uses second-order perturbation theory to correct the VSCF level, and is thus more accurate. It is shown by test calculations for a series of amino acids and peptides that the mean deviation of VSCF from VSCF-PT2 frequencies decreases for an increasing number of modes N, the decrease scaling roughly with log N. It is conjectured that the result is a manifestation of improved mean accuracy of VSCF as a mean-field approximation, a consequence of increased averaging with increasing numbers of modes. There is no systematic increase in VSCF accuracy with N for individual vibrational transitions. Increased accuracy of VSCF with N is found for certain groups of transitions, e.g., N-H stretches. The results are expected to be useful in choosing methods for spectroscopy calculations of extended systems such as large peptides, proteins, and nucleic acids.},
	issn = {1932-7447},
	doi = {10.1021/jp105066a},
	author = {Pele, Liat and R Benny Gerber}
}
