Title: FELIX-2.0: New version of the finite element solver for the time dependent generator coordinate method with the Gaussian overlap approximation,
Abstract: The time-dependent generator coordinate method (TDGCM) is a powerful method
to study the large amplitude collective motion of quantum many-body systems
such as atomic nuclei. Under the Gaussian Overlap Approximation (GOA), the
TDGCM leads to a local, time-dependent Schrödinger equation in a
multi-dimensional collective space. In this paper, we present the version 2.0
of the code FELIX that solves the collective Schrödinger equation in a finite
element basis. This new version features: (i) the ability to solve a
generalized TDGCM+GOA equation with a metric term in the collective
Hamiltonian, (ii) support for new kinds of finite elements and different types
of quadrature to compute the discretized Hamiltonian and overlap matrices,
(iii) the possibility to leverage the spectral element scheme, (iv) an explicit
Krylov approximation of the time propagator for time integration instead of the
implicit Crank-Nicolson method implemented in the first version, (v) an
entirely redesigned workflow. We benchmark this release on an analytic problem
as well as on realistic two-dimensional calculations of the low-energy fission
of Pu240 and Fm256. Low to moderate numerical precision calculations are most
efficiently performed with simplex elements with a degree 2 polynomial basis.
Higher precision calculations should instead use the spectral element method
with a degree 4 polynomial basis. We emphasize that in a realistic calculation
of fission mass distributions of Pu240, FELIX-2.0 is about 20 times faster than
its previous release (within a numerical precision of a few percents).