  H-wave is an open-source software package for performing the Hartree--Fock
approximation (HFA) and random phase approximation (RPA) for a wide range of
Hamiltonians of interacting fermionic systems. In HFA calculations, H-wave
examines the stability of several symmetry-broken phases, such as
anti-ferromagnetic and charge-ordered phases, in the given Hamiltonians at zero
and finite temperatures. Furthermore, H-wave calculates the dynamical
susceptibilities using RPA to examine the instability toward the
symmetry-broken phases. By preparing a simple input file for specifying the
Hamiltonians, users can perform HFA and RPA for standard Hamiltonians in
condensed matter physics, such as the Hubbard model and its extensions.
Additionally, users can use a Wannier90-like format to specify fermionic
Hamiltonians. A Wannier90 format is implemented in RESPACK to derive ab initio
Hamiltonians for solids. HFA and RPA for the ab initio Hamiltonians can be
easily performed using H-wave. In this paper, we first explain the basis of HFA
and RPA, and the basic usage of H-wave, including download and installation.
Thereafter, the input file formats implemented in H-wave, including the
Wannier90-like format for specifying the interacting fermionic Hamiltonians,
are discussed. Finally, we present several examples of H-wave such as
zero-temperature HFA calculations for the extended Hubbard model on a square
lattice, finite-temperature HFA calculations for the Hubbard model on a cubic
lattice, and RPA in the extended Hubbard model on a square lattice.
