Gaussian

F L P R website, discussed version: G16 A.03

Credits: Sergey Matveev and Victor Vysotskiy (installation, scripts)

Installation: Linux

Locate executables, edit your user initialization file, create gaussian directory, and learn how to submit a job.
Job submission scripts: thinc cluster (MO, MO2, NO, MOPBC), Magnus cluster, MOAB example
PBS submission command: qsub gaussian/_pbs -N test1 -l nodes=1:ppn=4,mem=13gb,ddisk=40gb,walltime=25:00:00,feature=avx,epilogue=$HOME/bin/epilogue.sh -q batch
SLURM submission command: sbatch -J test1 -c 8 -t 12:00:00 gaussian/_pbs
Example of Gaussian run script without PBS: example
Sample input file: test1.gau

Install. Do not use special symbols in path to executables. Properly allocate Scratch folder.
Set environment variable GAUSS_EXEDIR.
Run Gaussian as follows: %GAUSS_EXEDIR%\g09 inputfile outputfile (output filename is optional).
Edit and copy gaussian.bat to the program folder (or any other location).
Associate gau-files with gaussian.bat. For this purpose you can edit and use these file associations.

Gaussian is very sensitive to the number of empty lines in the input file, i.e. wrong number might lead to misinterpreted input. In particular, some Windows versions require nonempty title in input file.

Gaussian requires explicit setting of nproc and mem. See Memory Use.
Fortran code for extracting individual records from Gaussian chk- and rwf-files. You may use this test file. See also sample batch script.
Python utilities for reading transition density matrices from record 633: zip.
Examples of how to produce natural orbitals and natural transition orbitals readable by Jmol directly from the Gaussian output, including Jmol scripts for making jpeg-images of these orbitals: zip.
Less convenient but more universal is to generate a cube file: cubegen 0 mo=homo in.fchk out.cube -2 h, and then read it by Jmol.

Start with chk-file converged for S0 state, smaller basis of the same series, or similar functional.
Change algorithm: scf(qc,intrep) or scf(symm) if specific symmetry is needed.
Maybe shake geometry and take the lowest energy result.