Open AccessExploring the effect of anharmonicity of molecular vibrations on thermodynamic properties
Author(s) -
Bosiljka Njegic,
Mark S. Gordon
Publication year - 2006
Publication title -
the journal of chemical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.071
H-Index - 357
eISSN - 1089-7690
pISSN - 0021-9606
DOI - 10.1063/1.2395940
Subject(s) - anharmonicity , vibrational partition function , molecular vibration , normal mode , vibration , enthalpy , chemistry , thermodynamics , normal coordinates , hot band , harmonic , harmonic oscillator , cartesian coordinate system , vibrational energy , entropy (arrow of time) , molecule , molecular physics , physics , quantum mechanics , organic chemistry , geometry , mathematics
Thermodynamic properties of selected small and medium size molecules were calculated using harmonic and anharmonic vibrational frequencies. Harmonic vibrational frequencies were obtained by normal mode analysis, whereas anharmonic ones were calculated using the vibrational self-consistent field (VSCF) method. The calculated and available experimental thermodynamic data for zero point energy, enthalpy, entropy, and heat capacity are compared. It is found that the anharmonicity and coupling of molecular vibrations can play a significant role in predicting accurate thermodynamic quantities. Limitations of the current VSCF method for low frequency modes have been partially removed by following normal mode displacements in internal, rather than Cartesian, coordinates.
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