How to find resonance width in an output file?

Questions
#1

I am working on one of the q-chem examples (Input for a standard CAP/EA-ADC(3) calculation of the dinitrogen anion’s pg2 resonance). I would like to learn how to calculate resonance width or extract it from the output? I found some explanations (7.11.8 CAP/ADC Methods for the Description of Metastable Electronic States‣ 7.11 Correlated Excited State Methods: The ADC( n ) Family ‣ Chapter 7 Open-Shell and Excited-State Methods ‣ Q-Chem 5.4 User’s Manual ,and Cookie Absent ), but I can not find this term (resonance width) in the output.

#2

Hello Farshad,

I just replied to you through email. However, I am posting the developer’s comments here for future reference. (Hat tip to Dr. Adrian L. Dempwolff)

Since the evaluation of CAP trajectories and the extraction of resonance
parameters (i.e., position and width) often requires very careful
fine-tuning of some associated parameters, a direct computation of the
quantities of interest after the electronic structure calculation would
not be very beneficial, since the whole calculation might have to be
repeated several times before a meaningful CAP trajectory has been
generated. For example, the CAP/EA-ADC(3) calculation of the example
took ~ 10 min, but the evaluation of a CAP trajectory usually only takes
a couple of seconds. Repeating the CAP/EA-ADC calculation over and over
again only because of changed trajectory parameters would thus just be a
waste of resources.

In the subspace-projected CAP formulation, which the CAP/ADC
implementation relies on, it is instead possible to analyze CAP
trajectories a posteriori using a separate program, which is indeed not
very complex, i.e., can be written in < 500 lines of python including a
Q-Chem output file parser and CAP trajectory plot output etc. All
needed input for sich a program is given in the Q-Chem output of the
CAP/EA-ADC(3) calculation, i.e., the (diagonal) matrix of EA-ADC(3)
eigenvalues (usually called H0, the real part of the subspace-projected
CAP/EA-ADC(3) matrix), and the CAP representation within converged
EA-ADC(3) states, which enters the CAP trajectory computation as
imaginary part (usually called W), scaled with the CAP stength eta.

Having said that, there are tools out there exactly designed for this
purpose. For example, see
[Analysis Tools — pyopencap documentation]:
The matrices as appearing in the CAP/EA-ADC(3) output can directly be
used to construct the CAPHamiltonian object.

#3

I am guessing you need to look for imaginary energy. The resonance width is an inverse of the imaginary part of the total energy.

You can read more about non-Hermitian extensions of quantum chemistry to describe electronic resonances here:
http://www.annualreviews.org/eprint/C6sRwNBvGirygawq2mGm/full/10.1146/annurev-physchem-052516-050622
and here: