DEHam (version 2.0)

Double Exchange Hamiltonian: Complete Version

(under GNU GENERAL PUBLIC LICENSE v2)

This program can perform Exact diagonalization calculations of various types of model Hamiltonians. It is especially optimized for the t-J (or Double Exchange) type model Hamiltonians. The core feature which the program is specialized for is the adressing of determinant in an efficient manner to quickly construct the Hamiltonian non-zero matrix-elements. Once the Hamiltonian is constructed in its sparse format, it is stored in distributed memory for all linear algebra operations.

The main work of diagonalizing the Hamiltonian is performed using PETSc and SLEPc helper functions. These functions return the eigenvectors which are not stored to disk by default due to their large size.

This project also contains subroutines which analyze the wavefunction in its distributed memory form and calculates the various observables. The output of the program are the energies and the various observables such as the total Spin, various Spin-Spin correlation functions, and one-and two-body density matrices.

Note: Caluculation of S2 can be deactivated to save memory and perform larger matrix diagonalizations.

Dependencies

1. PETSc

2. SLEPc

3. IGraph

4. slaterlib

Compiling

1. Configure with explicit paths of installation directories of PETSc and SLEPc.

./autogen.sh
./configure CFLAGS="-I{PATH-TO-INCLUDE-SLEPC-PETSC-FILES} " LDFLAGS="-L{PATH-FOR-LIBRARY-FILES} -lpetsc -lslepc -lpetsc -lslater -ligraph -lm"  CC=mpicc

2. Make the executable

make
make install

Using DEHamv2

1. The DEHamv2 program requires an input file which has is in the graphml format. A few sample files have been provided in the data/ directory.

2. running DEHam

mpiexec -n [nprocs] ./bin/ex1 -eps_nev 10 -f data/c8h8_mma.graphml 

Publications using this code

1. High-Spin Chains and Crowns from Double-Exchange Mechanism doi:10.3390/cryst6040039