**AHB1, program description**

SSE quantum Monte Carlo simulation of an isotropic S=1/2 Heisenberg model on
a simple cubic lattice in 1, 2, or 3 dimensions. An efficient operator-loop
update is used. The physical quantities calculated are: the internal energy,
the specific heat, the uniform magnetic susceptibility, the spin stiffness,
the staggered spin structure factor, and the staggered spin susceptibility.

**Fortran program files**
Complete simulation program

ahb1.f

Include-file for 'ahb1.f'

ahb1.h

Program for processing the output of 'ahb1.f'

ahb1res.f

**Summary of usage**

The full source code of the simulation program is in 'ahb1.f'. The program is
compiled for a user-fixed dimensionality and lattice size, which are both set
in the include-file 'ahb1.h'. The raw data generated by the simulation program
AHB1 should be processed by the program AHB1RES (file 'ahb1res.f'), which
calculates averages and statistical errors.

Details on how to run the program

**Useful references for algorithms used**

A. W. Sandvik, Phys. Rev. B 59, R14157 (1999)
[Introduces the SSE operator-loop update].

A. W. Sandvik, Phys. Rev. B 56, 11678 (1997)
[Discusses estimators for expectation values].
O. F. Syljuåsen and A. W. Sandvik, cond-mat/0202316 (to appear in Phys. Rev.
E) [Contains a detailed pedagogical discussion of the SSE algorithm].

**Credits**

Author: A. W. Sandvik

Cite references: A. W. Sandvik, Phys. Rev. B59, R14157 (1999)