Dipelm: A code to calculate photoionization observables

Table of Contents

• Introduction
• Input
  • File input
  • Namelist input
• Output
  • Randomly oriented molecules
  • Oriented molecules

Introduction

Dipelm calculates:

• Photoionization cross sections and asymmetry paramters for randomly oriented molecules.
• Molecular frame photoionization dipoles (MFDip) and photoelectron angular distributions (MFPAD).
• Lab frame photoionization dipoles (LFDip) and photoelectron angular distributions (LFPAD).

Input

File input

Dipelm takes partial wave transition moments produced by rsolve (in the routine comppwd) as input

Namelist input

Dipelm has one required namelist, &dipelminp, and two optional namelists &smooth and &orient.

&dipelminp controls input file data. One can also select a subset of states for randomly oriented molecule observables (default behaviour is to use all states).

&smooth controls smoothing of the partial wave dipoles prior to calculation of observables. This can be useful if one wants to remove narrow unphysical pseudoresonances (narrow real resonances will also be removed). For dense energy grids and many partial wave channels this can take sometime. Only the subset of states chosen in &dipelminp will be smoothed.

&orient controls calculation of oriented observables. Default behaviour is to calculate the molecular frame photoionization dipoles and angular distributions, which are resolved in initial and final state, photon energy, and photoelectron direction. Only the MFPAD are output unless otherwise requested. Optionally, lab frame dipoles and angular distributions for a range of orientations will be calculated. File sizes can quickly become very large with this last option, so some restraint with the angular grids (alpha, beta, gamma, theta, phi) must be shown.

[&dipelminp, &smooth, &orient]

Output

All output files containing observables are prepended with photo_

Randomly oriented molecules

By default the output files generated are:

• photo_total_xsec: Total photoionization cross section for all neutral states.
• photo_xsec: Partial photoionization cross sections for all pairs of ion and neutral states
• photo_beta_1c: Dichroic parameter (circular polarization) for all pairs of ion and neutral states
• photo_beta_2l: Asymmetry parameter (linear polarization) for all pairs of ion and neutral states
• photo_beta_2c: Asymmetry parameter (circular polarization) for all pairs of ion and neutral states

The first column is the photon energy (eV), following columns correspond to the observable in question for each ion state (in energy order by default) for ion state resolved observables. Each neutral state starts a new block, again in energy order.

Optionally, each state pair can be output to a seperate file, in this case the file names above are appended with _ion_state_i_neutral_state_j, where i and j index the ion and neutral states respectively (in energy order by default). Each file then consists of two columns, the photon energy and the observable. photo_total_xsec is appended with only _neutral_state_j.

Oriented molecules

If oriented observables are calculated, the output files generated are:

• photo_MFPAD_ion_state_i_neutral_state_j: The MFPAD (default)
• photo_MFDip_ion_state_i_neutral_state_j: The MFDip (optional)
• photo_LFPAD_ion_state_i_neutral_state_j: The LFPAD (optional)
• photo_LFDip_ion_state_i_neutral_state_j: The LFDip (optional)

Photon energies Currently the y, z, and x cartesian components of the dipoles are output in the dipoles files (in that order). These correspond to y, z and x linearly polarized light directions in the PAD files. Circular polarization is not currently implemented (but will be in a future release). If it is required it can be obtained by post-processing of the dipole files to transform the cartesian components to the spherical basis, then taking the modulus squared and multiplying by the photon energy dependent coefficient (see dipole_procs::calculate_MFPAD). Photon energy is in Hartree, in contrast to randomly oriented molecule observables.

The files are in binary stream format, to read and plot them see the following:

Python read and plot example