  In order to simulate open quantum systems, many approaches (such as
Hamiltonian-based solvers in dynamical mean-field theory) aim for a
reproduction of a desired environment spectral density in terms of a discrete
set of bath states, mimicking the open system as a larger closed problem.
Existing strategies to find a compressed representation of the environment for
this purpose can be numerically demanding, or lack the compactness and
systematic improvability required for an accurate description of the system
propagator. We propose a method in which bath orbitals are constructed
explicitly by an algebraic construction based on the Schmidt-decomposition of
response wave functions, efficiently and systematically compressing the
description of the full environment. These resulting bath orbitals are designed
to directly reproduce the system Green's function, not hybridization, which
allows for consideration of the relevant system energy scales to optimally
model. This results in an accurate and efficient truncation of the environment,
with applications in a wide range of numerical simulations of open quantum
systems.
