DEHam

Double Exchange Hamiltonian: Complete Version

(under GNU GENERAL PUBLIC LICENSE v2)

Dependencies

1. PETSc and SLEPc

2. IRPF90

Compiling

1. Export environment variables for PETSc and SLEPc

export PETSC_DIR=${PATH_TO_PETSC_INSTALLATION}
export SLEPC_DIR=${PATH_TO_SLEPC_INSTALLATION}
export C_INCLUDE_PATH+=:$PETSC_DIR/include/:$SLEPC_DIR/include:$PETSC_DIR/arch-linux2-c-debug/include/:$SLEPC_DIR/arch-linux2-c-debug/include
# The "arch-linux2-c-debug" directory can have different names depending on PETSC and SLEPC installation procedure.

2. Make the executable

make ex1

Using DEHam

1. The DEHam program requires an input file which has the topology of the Hamiltonian and the various parameters as explained below in a sample inputfile:

8     # The number of orbitals (total)
140   # The largest number of non-zero elements per row (Multiple of Ndet)
1     # The total number of processors used in parallel (Multiple of Ndet)
1     # The number of holes
0     # The isz (ms-1/2) value
true     # Restrict the hole to the 1'st (i.e. half of natom) Family of states. *false* for no restrictions
1,2,3,1,2,3,4,5,6,7 # The topology of the system is specified here
2,3,4,8,7,6,5,6,7,8 # first and second line contain the two sites linked
1,1,1,2,2,2,2,3,3,3 # third line contains the type of link (1 for t or J, 2 for K and 3 for none)
.1430,-0.20,0.0000  # The three types of links this line gives J, K
.1430,-0.20,0.0000  # 
-1.00,0.0,0.00      # This line gives t
0.,0.,0.,0.,0.,0.,0.,0.,0. # Energy of each orbital + one extra term
2                   # The total number of roots
1                   # I   The position of the first
1                   # I   SBox
1                   # I
1                   # I
1                   # II  The positions of the second
1                   # II  SBox
1                   # II
1                   # II
1                   # III
1                   # III The positions of the third
1                   # III SBox
1                   # III
1                   # positio of the hole
0                   # fix the position of the first hole during the CI
0                   # fix the position of the second hole during the CI
0                   # Print the wavefunction. It is stored in the FIL666 file after the run

2. running DEHam

mpiexec -n [nprocs] ./bin/ex1 input_file.inp

Sample Application

A 2D t-J model Hamiltonian description and setup for using DEHam to solve for few low lying states is provided in the notbooks folder. Please have a look about the details of using DEHam to study t-J Hamiltonians.

Publications using this code

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