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Luca Maidich
luca.maidich@gmail.com

a) As far as I know there is NOT an upper limit to the value of TIMLIM in $SYSTEM group, you can put whatever time you want keeping in mind that the value is taken by the system in minutes; so the first option could be to set the TIMLIM variable to a very big number (say 525600 i.e. the minutes in a year), in other words you should add this line to your input file.
$SYSTEM TIMLIM=525600 $END

b) You can increase the number of iterations using NSTEP variable in $STATPT group to a very big number.

c) You can do a "two step optimization" in which you use a coarser convergence criterion in a first step (say OPTTOL=1E-4 in $STATPT) and then, on the optimized geometry, you can tighten the OPTTOL to a smaller value depending on your needs. You can also operate on the convergence of the SCF cycle using the keyword NCONV=value in the $SCF group where value is an integer, this will set the convergence criterion of the SCF cycle to 10^(-value).

d) If you prefer to have more control on your optimization process without lowering your convergence criteria you can use "a kind of" restart option which consist in copying the last geometry and pasting it in a new file starting a new optimization process. Firefly has also an option that if it exceeds the maximum number of iterations (i.e. NSTEP in $STATPT) restart data are written in the PUNCH file.

Hope this helps, if you have other issues please do not hesitate in asking on the forum and if some keywords sounds weird to you please have a look at the manual that I'm attaching to this message.

Kind Regards
Luca

This message contains the 471 kb attachment [ INPUT_colated_1.pdf ] pdf version of Firefly 7.1.G manual.