Copyright (C) Jochen Autschbach, 2018-2025
Tools for calculating magnetic circular dichroism (MCD), magneto-chiral dichroism (MChD), and natural electronic circular dichroism (CD) and absorption spectra using data files generated by the RASSI program of the OpenMolcas quantum chemistry package. Other tools have been added over time, such as a code for the van Vleck magnetic susceptibility.
The programs, as set up, require a recent (ca. 2018 or later) version
of Molcas that has the RASSI PRPRint keyword to write dipole, spin,
and angular momentum matrix elements to files named dipole-X.txt,
spin-X.txt and angmom-X.txt, rescpectively, with X = 1,2,3 for the
Cartesian components x, y, z. We did this for two reasons:
Convenience, and to get machine precision data instead of parsing
the Molcas output. Program options are controlled by Fortran namelist input.
The namelist is called 'options' and read from a file
options.dat. For details see the code, esp. namelist-module.f90,
and comments below.
The code in this repository has been used previously for the following publications (and a few others):
Curran, D. J.; Ganguly, G.; Heit, Y. N.; Wolford, N. J.; Minasian, S. G.; Löble, M. W.; Cary, S. K.; Kozimor, S. A.; Autschbach, J.; Neidig, M. L., ‘Near-Infrared C-term MCD Spectroscopy of Octahedral Uranium(V) Complexes’, Dalton Trans. 2021, 50, 4853–4925. URL https://doi.org/10.1039/D1DT00513H
Atzori, M.; Ludowieg, H.; Cortijo, M.; Breslavetz, I.; Paillot, K.; Rosa, P.; Train, C.; Autschbach, J.; Hillard, E. A.; Rikken, G. L. J. A., ‘Validation of Microscopic Magneto-Chiral Dichroism Theory’, Science Advances 2021, 7, eabg2859 (7 pages). URL https://doi.org/10.1126/sciadv.abg2859
Fleischauer, V. E.; Ganguly, G.; Woen, D. H.; Wolford, N. J.; Evans, W. J.; Autschbach, J.; Neidig, M. L., ‘Insight into the Electronic Structure of Formal Lanthanide(II) Complexes using Magnetic Circular Dichroism Spectroscopy’, Organometallics 2019, 38, 3124–3131. URL https://doi.org/10.1021/acs.organomet.9b00315
Heit, Y. N.; Sergentu, D.-C.; Autschbach, J., ‘Magnetic circular dichroism spectra of transition metal complexes calculated from restricted active space wavefunctions’, Phys. Chem. Chem. Phys. 2019, 21, 5586–5597. URL https://doi.org/10.1039/C8CP07849A
Gendron, F.; Fleischauer, V. E.; Duignan, T. J.; Scott, B. L.; Löble, M. W.; Cary, S. K.; Kozimor, S.; Bolvin, H.; Neidig, M. L.; Autschbach, J., ‘Magnetic circular dichroism of UCl6− in the ligand-to-metal charge-transfer spectral region’, Phys. Chem. Chem. Phys. 2017, 19, 17300–17313. URL https://doi.org/10.1039/C7CP02572F
OpenMolcas is available from https://github.com/Molcas/OpenMolcas
Usage:
Run OpenMolcas with the following keywords in the SEWARD step
Angmom
0.0 0.0 0.0
AMFI
and with the following keywords in the RASSI step of the calculation:
MEES
MESO
SPIN
PRPRint
PROPerties
7
'AngMom' 1
'AngMom' 2
'AngMom' 3
'Mltpl 0' 1
'MltPl 1' 1
'MltPl 1' 2
'MltPl 1' 3
Use of the PRPRint keyword will cause operator matrix elements in
the basis of all RASSI spin-orbit coupled wavefunctions to be written
to ASCII text files named spin-1.txt, spin-2.txt, spin-3.txt,
angmon-1.txt etc., dipole-1.txt etc., for the x, y, and z
components (1,2,3). The relevant operators are those for the electron
spin, the electron orbital angular momentum, and the electron dipole
moment, respectively.
Run the script molcas-get-energies.sh provided in this repository
with the RASSI output file name as the argument to create a list of
state energies in file energies.txt:
molcas-get-energies.sh <rassi output file>
The programs being provided in this repository read Fortran namelist
input from a file options.dat along with the wavefunction data and
state energies provided in the files mentioned above. The states are
grouped into degenerate levels, where applicable, based on a threshold
set by the namelist input. Some of the options that can be set in
options.dat are as follows:
nstates (integer) : number of states, must match energies.txt
degen (integer) : ground state degeneracy. Set to 0 for autodetection
ddelta (real) : criterion for state degeneracy (Hartree)
temp (real) : temperature (K) for MCD/MChD C-term calculations
trange(1:2) (real): start/end temp. for susceptibility
oldspiny (logical): use Molcas spin-y convention pre-2020 (see code)
nstates must be provided, almost everything else is optional. The
temp variable must be defined and set to a value > 0 for the
MCD/MChD C-term codes to run without errors. The default value for
ddelta is 1E-5. States that have energies differing by no more than
ddelta are grouped into degenerate levels. The temp
setting is ignored by the susceptibility code. The trange setting is
ignored by the MCD/MChD C-term codes. The trange default is 1 to 301
K. The programs try to detect if unphysical values are given for the
most important options. However, proceed at your own risk.
Additional options are available for some of the functionality. Please
see the relevant source code files and example calculations for
explanations. Each of the executable programs goes through the same
initial steps to parse the namelist options and read the data
files. Some of the functionality requires also electric quadrupole
matrix elements, or the electric dipole and quadrupole data in
velocity form. See the example job ethene-twisted how to set this
up.