Partition function zeros for the two-dimensional using model IV

The boundaries of regions containing complex temperature zeros of the partition function of the two-dimensional Ising model on completely anisotropic triangular and quadratic lattices are investigated in detail. Numerical solutions of the boundary equations are presented for triangular lattices with interactions in the ratios 3 : 2 : 1 and 4 : 2 : 1. For general anisotropic triangular and quadratic lattices, the origins of “pinch-points”, at which the boundary lines intersect, is elucidated, and the relation of critical and disorder points to pure imaginary zeros, and their role in the classification of zeros, is analyzed. An explanation is given of why interior (non-boundary) complex solutions of the critical point equations can occur for triangular lattices.