IMPROVED PHASE-DIAGRAMS OF ASHKIN-TELLER MODEL

The phase diagram of the Askhim-Teller model in two dimensions is dete rmined. Numerical calculations are performed for the simple square L x L lattice using transfer matrix technique. Exploiting finite-size sca ling all unknown critical lines were obtained with good accuracy. An e xtended version of the Ashkin-Teller model is also considered within t he molecular field renormalization group method and the critical surfa ce for three-parameter odd-parity Hamiltonian is calculated.