SQDFT

SQDFT is a code for performing high-temperature Born-Oppenheimer Quantum Molecular Dynamics (QMD) in the framework of Kohn-Sham Density Functional Theory (DFT). While applicable at any temperature, the SQDFT code is most efficient at high temperature where the Fermi-Dirac distribution becomes smoother and density matrix becomes correspondingly more localized. SQDFT employs the O(N) infinite-cell Clenshaw-Curtis Spectral Quadrature (SQ) method, a technique that is applicable to metallic as well as insulating systems, is highly parallelizable to hundreds of thousands of processors, becomes increasingly efficient with increasing temperature, and provides results corresponding to the infinite crystal without the need of Brillouin zone integration.

Users of SQDFT are expected to cite the following publication: Suryanarayana, P., Pratapa, P.P., Sharma, A. and Pask, J.E., 2018. SQDFT: Spectral Quadrature method for large-scale parallel O (N) Kohn–Sham calculations at high temperature. Computer Physics Communications, 224, pp.288-298.

1. External Libraries: SQDFT uses the following external library:
   MVAPICH2 2.1, http://mvapich.cse.ohio-state.edu/news/
   The code has been tested using mvapich2/2.1 and intel/15.0 compilers, openmpi/1.8 and gcc/4.9.0, and IBM mpicxx-4.7.2.

2. Compilation: SQDFT can be compiled from within the "SQDFT" folder using the commands:

   make clean
make

   A successful compilation will lead to the creation of the executable "SQDFT/lib/sqdft"

3. Input files: SQDFT requires the following files as input:

   • ".input" - User options and parameters.
   • ".atoms" - Atomic information. In addition, SQDFT requires Troullier-Martins pseudopotential files as generated by the code "atom" (http://bohr.inesc-mn.pt/~jlm/pseudo.html).

4. Execution: SQDFT can be executed in parallel using the mpirun command. Sample PBS script files are available in "SQDFT/tests" folder. The ".input" and ".atoms" input files should be present in the root folder, and the corresponding pseudopotential files in the "./pseudopotential" subfolder. Example input files can be found in the "SQDFT/tests" folder.

   Example: To run a simulation on 8 processors with input files as "filename1.input" and "filename2.atoms", use the following command:

   mpirun -np 8 ./lib/sqdft -name filename1

5. User Guide: Please refer to the SQDFT User Guide ("SQDFTUserGuide.pdf" provided in "SQDFT/doc" subfolder) for more information on input and output files contents.

6. Tests: The "SQDFT/tests" folder contains two tests:

   • Al
   • LiH
     These tests can be executed using the mpirun command as described above. The alternative is to use the PBS script files that have been provided. The energies and forces in the resulting output files should be compared with the reference output files: results_Al and results_LiH given in Al and LiH tests folders, respectively. Note that all simulations should be executed from the root folder.

7. Brief Description of all files in SQDFT:

   • In "SQDFT/doc" folder

     SQDFTUserGuide.pdf : The user guide for SQDFT

   • In "SQDFT/inc" folder

     ds_sq.h : Header file containing information of all data structures
     func_sq.h : Header file declaring all the functions used in this code
     headers.h : Header file declaring all the standard header files required for this code

   • In "SQDFT/lib" folder

     sqdft : Executable created after the successful compilation of the code

   • In "SQDFT/pseudopotentials" folder

     Subfolder containing pseudopotential files for Aluminium, Hydrogen and Lithium

   • In "SQDFT/src" folder

     anderson.cpp : Functions for performing Anderson extrapolation
     deallocate.cpp : Function for de-allocating the memory
     energy.cpp : Functions for computing energy
     forces.cpp : Functions for computing the atomic forces
     initialize.cpp : Functions for initializion
     main.cpp : The main function
     md.cpp : Functions required for Quantum Molecular Dynamics (QMD)
     nonlocal.cpp : Functions for calculation related to the nonlocal projectors
     poisson.cpp : Functions for solving the Poisson's equation
     readfiles.cpp : Functions for reading and storing the inputs from the given input files
     scf.cpp : Functions required in the SCF iteration
     spline.cpp : Functions for doing the 1d cubic spline interpolation
     sq.cpp : Functions for performing Spectral Quadrature (SQ)

   • In "SQDFT/tests" folder

     Al : Input and output files for Al
     LiH : input and output files for LiH
     sqdft.pbs : PBS script file

   • In "SQDFT" folder

     README.md : This file
     makefile : The makefile to compile SQDFT