mirror of
https://github.com/LCPQ/DEHam
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114 lines
4.4 KiB
Markdown
114 lines
4.4 KiB
Markdown
[](http://dx.doi.org/10.5281/zenodo.20450)
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# DEHam
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Double Exchange Hamiltonian: Complete Version
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=============================================
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(under GNU GENERAL PUBLIC LICENSE v2)
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This program can perform Exact diagonalization calculations of various types of
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model Hamiltonians. It is especially optimized for the t-J (or Double Exchange)
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type model Hamiltonians. The core feature which the program is specialized for
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is the adressing of determinant in an efficient manner to quickly construct the
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Hamiltonian non-zero matrix-elements. Once the Hamiltonian is constructed in
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its sparse format, it is stored in distributed memory for all linear algebra
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operations.
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The main work of diagonalizing the Hamiltonian is performed using PETSc and
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SLEPc helper functions. These functions return the eigenvectors which are
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not stored to disk by default due to their large size.
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This project also contains subroutines which analyze the wavefunction in
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its distributed memory form and calculates the various observables. The
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output of the program are the energies and the various observables such as
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the total Spin, various Spin-Spin correlation functions, and one-and two-body
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density matrices.
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_Dependencies_
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---------------
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1. [PETSc](https://www.mcs.anl.gov/petsc/documentation/installation.html) and [SLEPc](http://slepc.upv.es/documentation/instal.htm)
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2. [IRPF90](https://github.com/scemama/irpf90)
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_Compiling_
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------------
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1. Export environment variables for PETSc and SLEPc
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```shell
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export PETSC_DIR=${PATH_TO_PETSC_INSTALLATION}
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export SLEPC_DIR=${PATH_TO_SLEPC_INSTALLATION}
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export C_INCLUDE_PATH+=:$PETSC_DIR/include/:$SLEPC_DIR/include:$PETSC_DIR/arch-linux2-c-debug/include/:$SLEPC_DIR/arch-linux2-c-debug/include
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# The "arch-linux2-c-debug" directory can have different names depending on PETSC and SLEPC installation procedure.
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```
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2. Make the executable
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```shell
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make ex1
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```
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[](https://asciinema.org/a/Ng3tSNDoWBkV5C9ZYvbxCW43B)
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_Using DEHam_
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---------------
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1. The DEHam program requires an input file which
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has the topology of the Hamiltonian and the various parameters
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as explained below in a sample inputfile:
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```python
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8 # The number of orbitals (total)
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140 # The largest number of non-zero elements per row (Multiple of Ndet)
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1 # The total number of processors used in parallel (Multiple of Ndet)
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1 # The number of holes
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0 # The Sz (nalpha-nbeta-1) (odd spins) value or (nalpha-nbeta) (even spins)
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true # Restrict the hole to the 1'st (i.e. half of natom) Family of states. *false* for no restrictions
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1,2,3,1,2,3,4,5,6,7 # The topology of the system is specified here
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2,3,4,8,7,6,5,6,7,8 # first and second line contain the two sites linked
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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 J in the second family of states)
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.1430,-0.20,0.0000 # The three types of links this line gives J, K, J2 along x axis
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.1430,-0.20,0.0000 # The three types of links this line gives J, K, J2 along y axis
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-1.00,0.0,0.00 # This line gives t
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0.,0.,0.,0.,0.,0.,0.,0.,0. # Energy of each orbital + one extra term
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2 # The total number of roots
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1 # I The position of the first
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1 # I SBox
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1 # I
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1 # I
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1 # II The positions of the second
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1 # II SBox
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1 # II
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1 # II
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1 # III
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1 # III The positions of the third
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1 # III SBox
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1 # III
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1 # positio of the hole
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0 # fix the position of the first hole during the CI
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0 # fix the position of the second hole during the CI
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0 # Print the wavefunction. It is stored in the FIL666 file after the run
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```
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2. running DEHam
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```shell
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mpiexec -n [nprocs] ./bin/ex1 input_file.inp
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```
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_Sample Application_
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--------------------
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A 2D t-J model Hamiltonian description and setup for using DEHam to solve for few low lying states
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is provided in the notbooks folder. Please have a look about the details of using DEHam to study
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t-J Hamiltonians.
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_Publications using this code_
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-------------------------------
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1. High-Spin Chains and Crowns from Double-Exchange Mechanism [doi:10.3390/cryst6040039](http://www.dx.doi.org/10.3390/cryst6040039)
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