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Manuscript Title: SPINSGA: a program package for evaluation of properties of spin-1/2 Heisenberg systems using the symmetric group approach.
Authors: N. Flocke
Program title: SPINSGA
Catalogue identifier: ADGN_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 106(1997)114
Programming language: Fortran.
Computer: SUN Sparc station.
Operating system: UNIX.
Word size: 32
Keywords: Solid state physics, Band structure, Spin-1/2 heisenberg, Systems, Antiferromagnetism, Symmetric group, Spin lattices, Statistical physics, Thermodynamics.
Classification: 7.3, 23.

Nature of problem:
This code computes different properties of spin-1/2 Heisenberg systems like ground state energies and wavefunctions and correlation functions.

Solution method:
The spin-1/2 Heisenberg matrix of a lattice is solved for the lowest eigenvalue and the corresponding eigenvector in a specific S, M-adapted spin basis. For this purpose a Davidson diagonalization procedure is employed. The product HC between the Hamiltonian matrix and the iteration vector is calculated in an implicit way, without ever setting up the H matrix. Once the eigenvector is found, several properties of the lattices can be calculated as expectation values.

Depends on the size of the Hamiltonian matrix to be treated. If it becomes too big for all data to be held incore, the program version 'SPINSGA__solve_roots-two-incore', depending on heavy I/O processing, must be used for finding the lowest roots.

Running time:
The example given in the test run input, required approximately 580 sec on a SUN Sparc 20.