<tt>MetaWave</tt>: A Platform for Unified Implementation of Nonrelativistic and Relativistic Wave Functions

MetaWave is a C++ template-based architecture designed for unified implementation of nonrelativistic and relativistic configuration interaction (CI) type of methods. It is highly modular, extendable, and efficient. This is achieved by decoupling the three distinct aspects of quantum chemical methods (i.e., nature of Hamiltonian, structure of wave function, and strategy of parallelization), thereby allowing for separate treatment of them through their internal type-trait and tagging systems furnished by C++ metaprogramming. Once the second-quantized Hamiltonians, whether nonrelativistic (spin-free) or relativistic (spin-dependent), are decomposed into topologically equivalent diagrams for a unified evaluation of the basic coupling coefficients between (randomly selected) spin-free or spin-dependent configuration state functions or Slater determinants incorporating full molecular symmetry (including single or double point group and spin or time reversal symmetry), the CI wave functions, whether built up with scalar or spinor orbitals, can be assembled with the same templates. As for parallelization, MetaWave supports both OpenMP and MPI, with the majority of the latter being translated automatically from its OpenMP counterparts. The whole structure of MetaWave is reviewed here, with some showcases for illustrating its performance.