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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.

Restrictions:
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.