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AngstromCube

DOI

AngstromCube is an experimental all-electron DFT application.
Using the Green functions formalism, near-sightedness allows
for linear-scaling and the projector augmented wave method (PAW), 
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)

AngstromCube logo

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 code that

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

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)
  • 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 none)
    • GPU acceleration (currently none)
    • 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
data matrix element files for SHO transforms between radial and Cartesian bases
test test scripts for certain modules
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
PAW Projector Augmented Wave
CPU Central Processing Unit
GPU Graphical Processing Unit
SHO Spherical Harmonic Oscillator
MPI Message Passing Interface
FFT Fast Fourier Transform
OMP OpenMP, Open Multi-Processing
TeX typesetting
Gf Green function
Wf Wave function (eigenstate)