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Thermodynamic molecular mechanics force field: Modified QCFF program
Author(s) -
Kar Mangalya,
Lenz Terry G.,
Vaughan John D.
Publication year - 1994
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.540151107
Subject(s) - dihedral angle , chemistry , force field (fiction) , internal rotation , thermodynamics , gibbs free energy , conformational isomerism , molecular geometry , computational chemistry , internal energy , bond length , molecule , physics , organic chemistry , quantum mechanics , hydrogen bond , mechanical engineering , engineering
The QCFF program originated by Warshel and Karplus 4a was modified to compute accurate thermodynamic properties S o , C p o , (H T o– H 0 o )/ T , and ΔH f ofor various acyclic and cyclic alkenes and alkadienes. Modifications consisted of adjusted bond angle, dihedral angle, bond stretch, and bond energy parameters that improved calculated vibrational frequencies, zero point energies, and thermodynamic functions. Supplemental torsional potential energy functions that were added to existing torsional functions led to greatly improved relative conformer energies and ΔH f 0values. It was shown that inclusion of hindered internal rotation leads to significantly better agreement of calculated thermodynamic functions with observed values for acyclic alkenes at high temperatures. The calculated thermodynamic properties of the alkenes and alkadienes were deemed sufficiently accurate for calculation of standard enthalpies and Gibbs free energies of gas phase chemical reactions at various temperatures. © 1994 by John Wiley & Sons, Inc.