A C++ library to perform efficient Exact Diagonalizations of quantum many body systems.

• Basic algebra of operators in quantum many-body systems
• Iterative linear algebra for computing eigendecompositions and time-evolutions (e.g. Lanczos algorithm)
• Local spin, t-J, or fermionic models
• Full support of generic space group symmetries
• parallelization both with OpenMP and MPI
• modern C++17 impementation simplifying usage

Clone this repository first. Afterwards, the xdiag library can be compiled using the standard CMake instructions

cmake -S . -B build
cmake --build build
cmake --install build

#include <xdiag/all.hpp>

using namespace xdiag;

int main() try {
  
  int n_sites = 16;
  int nup = n_sites / 2;
  Spinhalf block(n_sites, nup);

  // Define the nearest-neighbor Heisenberg model
  OpSum ops;
  for (int i = 0; i < n_sites; ++i) {
    ops += Op("HB", "J", {i, (i + 1) % n_sites});
  }
  ops["J"] = 1.0;

  set_verbosity(2);                // set verbosity for monitoring progress
  double e0 = eigval0(ops, block); // compute ground state energy
  
  Log("Ground state energy: {:.12f}", e0);
  
} catch (Error e) {
  error_trace(e);
}

The full documentation is available at awietek.github.io/xdiag.

author: Alexander Wietek license: Apache License 2.0