Problematic Convergence template (Gaussian):

The strategy is to describe solving convergence problems in a large production job by converging an SCF on a smaller approximate version of the job, using this as an initial guess for a moderate sized approximation, using this as initial guess for a larger job, etc., until you have a very good initial guess for the production job.

  1. set up input file (test1.com) for the lowest level job
    - specify the job type as RHF/STO-3G
    - be sure to provide a specific name (fe2co.chk) for the checkpoint file
  2. run the job using the input file above as:
    - run.s test1
    - if you are running in a scratch space different from where your input and output files are stored, ensure that your checkpoint file is copied back to the input/output directory for future use.
  3. copy over the previous input file (test1.com) to a new file (test2.com)
    - change the job type to RHF/6-31G
  4. run the new job as:
    - run.s test2
    - make sure the checkpoint file (fe2co.chk) is copied to the scratch directory at the start of the job, and returned to the input/output directory at the end
  5. copy over the previous input file (test2.com) to a new file (test3.com)
    - change the job type to B3-LYP/6-31G
  6. run the new job as:
    - run.s test3
    - make sure the checkpoint file (fe2co.chk) is copied to the scratch directory at the start of the job, and returned to the input/output directory at the end
  7. copy over the previous input file (test3.com) to a new file (fe2co.com)
    - change the job type to B3-LYP/6-31G*
  8. run the new job as:
    - run.s fe2co
    - make sure the checkpoint file (fe2co.chk) is copied to the scratch directory at the start of the job
************************************ test1.com ****************************
%chk=fe2co.chk
#P RHF/STO-3G

Tough convergence case

0 1
Fe1
 Fe2  Fe1   R1
 C    Fe1   R2   Fe2   A1
 O    C     R3   Fe1   A2   Fe2   A3
  Variables:
 R2=2.382524
 R3=1.143116
 A1=75.336242
 A2=63.720728
 A3=0.00
  Constants:
 R1=2.52

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