By including third- and fourth- order phonon anharmonic interactions terms into two-sublattice pseudospin-lattice coupled mode model, expressions for shift, width, soft mode frequency, dielectric constant and loss tangent have been evaluated for ferroelectric TGSe crystal. The method of retarded double- time thermal Green?s function has been used for derivation. Model values of physical quantities are fitted in expressions for soft mode frequency, shift, width, dielectric constant and loss tangent. Temperature dependence of these quantities has been numerically calculated. Theoretical results were compared with experimental results of available literature.
Green?s function, Dielectric, Anharmonic, Pseudospin, Loss tangent