AngstromCube

AngstromCube is an experimental all-electron Density Functional Theory (DFT) application.
Using the Green functions (Gf) formalism, near-sightedness allows
for linear-scaling and the Projector Augmented Wave (PAW) method, 
in particular the revised PAW method, see Paul F. Baumeister and Shigeru Tsukamoto,
  [proceedings of PASC19](https://dl.acm.org/doi/10.1145/3324989.3325717)

Setup

module --force purge
module load Stages/2025 imkl/2024.2.0 NVHPC/24.9-CUDA-12 CUDA/12 OpenMPI/5.0.5 CMake/3.30.3
rm -rf build
cmake . -B build -DHAS_MKL=ON -DHAS_MPI=ON -DHAS_FFTW=ON -DHAS_OPENMP=ON -DHAS_TFQMRGPU=ON
make -C build -j

Depending on your system of choice, you may need to switch some of these options to OFF. On JSC systems (Jülich Supercomputing Centre) we can try it with the given module environment.

Name The name refers to a cube with edge length 1 Angstrom which is abbreviated \AA in TeX code. This is because always 4x4x4 real-space grid points are grouped for performance which corresponds to roughly one \AA^3

Principles The idea is to have a DFT code that

• is highly parallel and can make use of GPUs
• does not require more input than the atomic coordinates
• can scale linearly with the volume

Current Status

• These features are ready:
  • MPI parallelization of parallel_potential and tfQMRgpu Green function solver
  • total energy calculation
  • complex wave functions, complex Green functions, k-points
  • boundary conditions for Wfs: periodic and isolated, for Gf also repeat and vacuum
  • non-magnetic potential generation
  • MPI parallel Poisson solver for the electrostatics (no preconditioner)
  • SHO-projector PAW with all-electron atoms (currently only non-magnetic)
  • GPU acceleration (CUDA support)
• These features are planned but have so far not been addressed:
  • different versions of LDA, GGA, meta-GGA (currently only LDA implemented)
  • efficient eigensolver for the grid Hamiltonian (currently inefficient subspace rotation method)
  • OpenMP parallelization (currently only in some places)
  • forces (currently none)
  • self-consistency convergence criteria (currently we set the number of iterations)
  • magnetism, collinear and non-collinear (currently only non-magnetic)
• Some features are build in only for development purposes:
  • a stable FFT Poisson solver for the electrostatic problem (serial only)
  • plane wave basis set using a dense matrix eigensolver (LAPACK) or iterative (in development)
  • dense eigensolver for the real-space grid Hamiltonian (expensive)
• These features are not intended to be implemented ever:
  • strain calculation
  • exact exchange
  • phonons

Directories The root folder of this repository contains the following directories:

Directory	Purpose
src	source folder for C++ and CUDA C++ sources
include	source folder for C and C++ header files
doc	documentation folder including manual and theory notes
doc/cho	documentation and sources for the Circular Harmonic Oscillator (CHO) basis
data	matrix element files for SHO transforms between radial and Cartesian bases
test	test scripts for certain modules
test/geo	some atom geometries for input
external	put third party libraries here
interfaces	examples for the libliveatom.so library in C, Fortran90, Julia and Python
tools	experimental scripts in Julia and Rust (programming languages)
ref	reference outputs of certain unit tests

Abbreviations

Abbr.	Explanation
DFT	Density Functional Theory
XC	Exchange-correlation
LDA	Local Density Approximation
GGA	Generalized Gradient Approximation
Wf	Wave function (eigenstate)
Gf	Green function
PAW	Projector Augmented Wave (method)
SHO	Spherical Harmonic Oscillator
CPU	Central Processing Unit
GPU	Graphical Processing Unit
MPI	Message Passing Interface
FFT	Fast Fourier Transform
OMP	OpenMP, Open Multi-Processing
TeX	LaTeX typesetting