GAMESS TIPs and TRICKs

Get your GAMESS T-Shirts

Naming Scheme

• Need some suggestions on how to name your files?
  • (S,T,etc.)##-(name)-(opt,spe,hes,sad)-(rhf,uhf,rohf,mp#).inp
    • (S,T,etc.) - singlet, triplet, ..., the multiplicity of the system
    • ## - the charge of the system ...,-1, 0, +1, ...
    • (name) - you can specify the name of the compound or something short like an important functional group
    • (opt,spe,hes,sad) - the operation you are performing, optimization, single point energy, hessian, saddle point search
    • (rhf,uhf,rohf,mp#) - the level of theory
    • Example: S0-si-h-opt-rhf-mp2.inp

Memory

• 1 MWORD = 1 000 000 WORDS
• X MWORDS = Y RAM in MB / 8

Geometry Optimization

• If you want to perform geometry optimizations using OPTTOL=10^-6 you should do the following:
  • Perform geometry optimizations using OPTTOL=10^-5 to obtain some geometry A
  • Then perform geometry optmizations on geometry A using OPTTOL=10^-6

Transition State Searches

• The most important tip: RUNTYP=SADPOINT
• !!DO NOT USE RUNTYPE=OPTIMIZE if you are searching for a transition state!!
• Option 1: Use MacMolPlt to produce a Linear Least Motion (LLM) path between two frames (one frame being your reactants and another frame being your products) note that you have to be on the first (leftmost) frame in order to be able to select MOLECULE > CREATE LLM PATH. Perform a saddle point run at either frame 25, 50, or 75.
• Option 2: Open up a log file from a HESSIAN job (zero imaginary frequencies so that it is characterized as a local minimum) and look at all the normal modes from SUBWINDOW > FREQUENCIES. Pick some modes that may coorespond to a motion in the direction of your products. At this mode go to VIEW > OFFSET ALONG MODE and select a value between 100% - 200% (I've found 125% - 150% to work out well). Perform a saddle point run at these offset coordinates.
• If All Else Fails: If you are unsuccessful with Option 1 and Option 2 then you may want to augment Option 1 or Option 2 with the following:
  $STATPT IHREP=1 $END
  This line will invoke GAMESS to recompute the HESSIAN after ever step. While this is time consuming - it may be your best bet if you are lacking some chemical intuition OR if you are dealing with a really complex system!

Basis Sets

• + : one set of diffuse s- and p- functions on HEAVY ATOMS
  • GAMESS: $BASIS DIFFSP=.TRUE. $END
• ++ : diffuse s- function is added to hydrogens on top of the + defintion
  • GAMESS: $BASIS DIFFSP=.TRUE. DIFFS=.TRUE. $END
• * : add d-polarization function on HEAVY ATOMS
  • GAMESS: $BASIS NDFUNC=1 $END
• (d) : add d-polarization function on HEAVY ATOMS
  • GAMESS: $BASIS NDFUNC=1 $END
• ** : add d-polarization and p-polarization functions on HEAVY ATOMS
  • GAMESS: $BASIS NDFUNC=1 NPFUNC=1 $END
• (d, p) : add d-polarization and p-polarization functions on HEAVY ATOMS
  • GAMESS: $BASIS NDFUNC=1 NPFUNC=1 $END
• (f) : add f-polarization functions on HEAVY ATOMS
  • GAMESS: $BASIS NFFUNC=1 $END