# PHON: A program to calculate phonons using the small displacement method

## Description

Abstract The program phon calculates force constant matrices and phonon frequencies in crystals. From the frequencies it also calculates various thermodynamic quantities, like the Helmholtz free energy, the entropy, the specific heat and the internal energy of the harmonic crystal. The procedure is based on the small displacement method, and can be used in combination with any program capable to calculate forces on the atoms of the crystal. In order to examine the usability of the method, I present he... Title of program: PHON Catalogue Id: AEDP_v1_0 Nature of problem Stable crystals at low temperature can be well described by expanding the potential energy around the atomic equilibrium positions. The movements of the atoms around their equilibrium positions can then be described using harmonic theory, and is characterised by global vibrations called phonons, which can be identified by vectors in the Brillouin zone of the crystal, and there are 3 phonon branches for each atom in the primitive cell. The problem is to calculate the frequencies of these phonons ... Versions of this program held in the CPC repository in Mendeley Data AEDP_v1_0; PHON; 10.1016/j.cpc.2009.03.010 This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2019)