FORTRAN code for the Gamma function

89 lines, 2878 bytes

The excitation probability distribution for microcanonical energies

The one-particle excitation probability distribution for states in a microcanonical ensemble (fixed number of particles, fixed energy, and fixed volume) is not given by the exponential Boltzmann distribution except in the limit of an infinite number of particles. The correct distribution, at least in many cases, is accurately approximated by a ratio of two Gamma functions. The FORTRAN code indicated here will evaluate the natural logarithm of the Gamma function and its first two derivatives. The accuracy is approximately 14 decimal places. The method used is Pade' approximants to the asymptotic series for large arguments and recursion downward.

These results are discussed in J. Chem. Phys. 117, 5564-5575 (2002) with further application for the case of hard spheres in J. Chem. Phys. 125, 164102 (2006).

for questions or comments contact

Randall B. Shirts
Department of Chemistry and Biochemistry
Brigham Young University
Provo, UT 84602

E-Mail Address: randy_shirts@byu.edu

Office Telephone Number: (801) 422-4290

FAX Number: (801) 422-0153

Office Room Number: C312 BNSN, BYU campus

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