DEHam

Double Exchange Hamiltonian: Complete Version

(under GNU GENERAL PUBLIC LICENSE v2)

1. Dependencies

1. PETSc and SLEPc

2. IRPF90

3. Compiling

4. Export environment variables for PETSc and SLEPc

```shell
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

```shell
make ex1
```

3. 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:

```python
140                 # The total number of determinants
7                   # The largest number of non-zero elements per row
2                   # The number of processors used in parallel
1                   # The number of holes
0                   # The isz (ms-1/2) value
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, 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
```

2. running DEHam

```shell
mpiexec -n [nprocs] ./ex1 inpfile 
```

4. Publications using this code

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