Speeding up ADC(2) calculations

Questions
#1

Hello,

I need to perform scans of excited states along some normal modes using ADC(2). Due to the volume of jobs I must process, I was wondering if there are any key points that I am missing to speed up the calculations, beyond assigning threads and memory. My current $rem section is:

METHOD ADC(2)
BASIS aug-cc-pVTZ
EE_SINGLETS 26
CC_SYMMETRY FALSE
ADC_DAVIDSON_MAXITER 500
BASIS_LIN_DEP_THRESH 4

MEM_TOTAL 64000
MEM_STATIC 2000

I could reduce the number of states to 20, but I would prefer to keep as many as possible. Additionally, I needed to set BASIS_LIN_DEP_THRESH because certain geometries cause the SCF to misbehave, ADC_DAVIDSON_MAXITER to ensure that my excited states are converged, and CC_SYMMETRY FALSE since scanning breaks the symmetry of the molecule.

Thank you in advance for any advice!

#2

You can try RI with ADC,
https://manual.q-chem.com/latest/sec_ADC_RI.html

In addition, for your SCF linear dependency problem a better solution (as compared to BASIS_LIN_DEP_THRESH) is to increase THRESH, e.g., to 14. That is what is recommended for diffuse basis functions, here:
https://doi.org/10.1021/acs.jpca.4c00283

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