# Effective Core Potentials for Calculations of Continuum Spectra of Molecules Using the Molecular R‑Matrix Method

## TL;DR

This paper introduces a method to use effective core potentials in molecular calculations for plasma modeling, enabling accurate simulations of electron collisions and photoionization.

## Contribution

The paper presents a novel implementation of ECPs in the UKRmol+ suite for continuum spectral calculations.

## Key findings

- ECP integrals over B-spline orbitals were derived and implemented for molecular calculations.
- Sample calculations for electron collisions and photoionization of various molecules were successfully performed.
- The method is applicable to large targets and high-energy electrons in plasma modeling.

## Abstract

Implementation of effective core potentials (ECPs) into
the molecular
scattering suite UKRmol+ is presented together with a set of calculations
for a range of targets relevant for plasma modeling. Continuum description
in scattering and photoionization calculations for large targets or
high-energy electrons often requires the use of numerical continuum
functions and the associated molecular integrals. We derive expressions
for ECP integrals over B-spline-type orbitals using their momentum-space
representation and describe their implementation. Sample calculations
are presented for electron collision with ethylene (C2H4), bromine (Br2), silicon tetrabromide (SiBr4), and tungsten hydride (WH), as well as photoionization of
methyl iodide (CH3I).