Thermo field Monte Carlo and transfer-matrix methods in quantum systems

Masuo Suzuki

T. Tsuzuki

An improved transfer matrix method is proposed for calculating the partition function of quantum spin systems, which is expressed by the M-th approximant of the Suzuki-Trotter transformation with Trotter number M. The point is to incorporate the symmetry property of the Trotter subsystem in calculation. The size of our transfer matrix is reduced very much. Thermodynamics is described by the maximum eigenvalue of the transfer matrix. Our method is applied to the XY model with spin 1/2. We consider the cases of pair and tri spin decompositions with Trotter number up to 4 (M≤4). We can do our calculation analytically in those cases. In the pair spin decomposition we find results which have been obtained by the Monte Carlo simulation and by a transfer matrix method by computer. We find nice results in the tri spin decomposition. Our result in the case M=4 is as good as the result in M=8 by the previous Monte Carlo simulation on comparing them with the exact result of Katsura.

Masuo Suzuki

The Quantum Transfer Matrix and Its Application to Quantum Spin Chains (K Kubo) Transfer Matrices in Quantum Many-Body Systems (T Koma) Monte Carlo Calculations of Elementary Excitation (M Takahashi) The Decoupled Cell Method of Quantum Monte Carlo Calculation (S Homma) Decoupled Cell Monte Carlo Study of the Critical Properties of the Spin-1/2 Ferromagnetic Heisenberg Model in Three Dimensions (R J Creswick & C J Sisson) Variational Monte Carlo Studies of Correlated Electrons (H Shiba) Quantum Monte Carlo Simulation of Multiband Fermion Systems and Its Application to Superconductivity (K Kuroki & H Aoki) Quantum Monte Carlo in the Infinite Dimensional Limit (M Jarrell et al) Aspects of the Sign Problem (J H Samson) Ground-State Projection Using Auxiliary Fields (S Fahy) Fermion Simulations of Correlated Systems (M Imada) Dirty Bosons in 2D: Phases and Phase Transitions (N Trivedi & M Makivi'c). (Part Contents).

Masatoshi Imada, Minoru Takahashi

A quantum transfer matrix method is proposed and examined. To obtain finite temperature properties, a small number of Monte Carlo samples for the trace summation is taken without the Monte Carlo sampling of the path integral. We introduce the method of a random orthonormal base in the Monte Carlo sampling. This makes it possible to investigate larger size systems than the exact diagonalization. An advantage of this method is that it does not have negative sign difficulty in the path integral as contrast to the usual quantum Monte Carlo method. A quantum molecular dynamics method is also proposed to investigate dynamical correlation functions.

H. DeRaedt, Ad Lagendijk, Pedro de Vries