Sum and density of states of polyatomic systems with hindered rotors

✍ Scribed by Forst, Wendell

• Book ID: 102649043
• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 636 KB
• Volume: 17
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/(sici)1096-987x(199606)17:8<954::aid-jcc4>3.0.co;2-q

✦ Synopsis

The density or sum of states for a collection of independent oscillators, free rotors, and one-dimensional hindered rotors is obtained with good accuracy by numerical inversion of the corresponding total partition function by the method of steepest descents. The hindered-rotor partition functions are used in both classical and quantum forms, the latter in the approximation proposed by Truhlar [ J. Comput. Chern., 12, 266 (1991)l. The numerical inversion compares well with analytical results obtained in a simple artificial case and also with an exact count of states in a large ethane-like system. Inversion of the hindered-rotor classical partition function is shown to lead to a somewhat different energy dependence of the sum or density of states, relative to the quantum counterpart, which is considered to be a more realistic representation. The routines presented are simple and fast enough to be of use in microcanonical rate calculations.