I am very interested in reproducing results of the your paper (J. Chem. Theory Comput. 2013, 9, 4495−4506), but cannot overcome one problem.
In the paper MEP (in CASSCF and CASPT2 level) is calculated in molcas, but I hope it is technically realizable in FF also.
As far as I understand, GS2 method is not suitable as it requires exact Hessian, that hardly can be obtaited in SA-calculations. At first I tried GS2, but the direction if minimum imaginary mode of FC excited state is far from the expected direction, so IRC goes in undesirable way.
Now I am trying RK4, but for PSB3 cation (from the paper) and analogous simple flat molecules MEP goes down with retaining the skeleton planarity and finally stops without changing the skeleton dihedral.
Obviously it stops because of being trapped in the valley of PES. The problem is to force the molecule go in the direction of bond rotation. I tried a lot of trivial ways to solve this problem, here is my last input:
$CONTRL SCFTYP=MCSCF RUNTYP=IRC ICHARG=+1 INTTYP=HONDO D5=1 ICUT=11
ICHARG=+1 NZVAR=1 $END
$ZMAT DLC=1 AUTO=1 $END
$SYSTEM TIMLIM=300000 MWORDS=300 $END
$BASIS GBASIS=n31 NGAUSS=6 NDFUNC=1 $END
$GUESS GUESS=MOREAD NORB=89 $END
$IRC PACE=RK4 SADDLE=0 STRIDE=0.05 NPOINT=300 $END
$STATPT METHOD=GDIIS OPTTOL=1D-4 NSTEP=300 DXMAX=0.5 TRMIN=0.1 $END
$DET CVGTOL=1D-8 NCORE=16 NACT=5 NELS=6 PURES=0 NSTATE=9
$MCSCF METHOD=DM2 ACURCY=1D-7 ENGTOL=1D-12 CISTEP=ALDET NTRACK=6 ISTATE=3 $END
$TRANS CUTTRF=1D-13 $END
$CIINP CASTRF=1 $END
... molecule is almost the same, but instead of H2C=CH-CH=CH-CH=NH2+ it is H2N-CH=CH-CH=NH2+
Could you, please, advice some tricks for solving this problem within FF?
[ This message was edited on Thu Jun 25 '15 at 4:52am by the author ]