# Charge and spin multiplicity change in IRC search

I have successfully isolated the TS for a radical cation catalysed C-C bond formation using Gaussian with input

1 2


for charge and spin multiplicity.

But when I do an IRC search with the correct input for charge and spin multiplicity (1 2 as above), the IRC log files terminate normally but when seen on GaussView, it says the molecule is neutral with singlet spin.

Is this a problem with GaussView? Will it affect the interpretation of the IRC in any way? In other words, does the IRC search still occur on the doublet PES or has it (somehow) gone to the singlet PES?

In other words, does the IRC search still occur on the doublet PES or has it (somehow) gone to the singlet PES?

You could check that by looking at the output. Right at the end of each and every SCF optimization Gaussian prints a block that starts with SCF Done and contains information about energy of the state to which SCF converged and its total spin. For instance, below is one such block in the results of test170 calculations from Gaussian 09 test set:

 SCF Done:  E(UHF) =  -40.1568456632     A.U. after   10 cycles
Convg  =    0.6432D-08             -V/T =  1.9978
<Sx>= 0.0000 <Sy>= 0.0000 <Sz>= 0.5000 <S**2>= 0.7832 S= 0.5165


Now, regarding GaussView, interestingly, it also wrongly shows that the state is singlet and not a doublet for that test job. Besides, GaussView reports the following when opening the output:

Unresolvable inconsistency between charge and multiplicity and orbital occupancies. Orbital data will be ignored.

Honestly speaking, I suspect that is a bug, because while reading the output I could not see any inconsistencies. I've tried few other IRC jobs on radicals form the Gaussian test set (test171, test452, test453) and GaussView always reports that a state is singlet when in fact it is a doublet. Moreover, in some cases GaussView even failed to read all the steps of a normally terminated IRC calculation. So, the only inconsistency I've noticed so far is that GaussView could not always correctly read Gaussian outputs of IRC calculations on states that are not singlets.

• Hi Wildcat, thanks for your reply. Yes, indeed when i open my normally terminated log file, i get the same warning as you have got. I did not find any inconsistency in the gaussian output too. I think you must be right that it is a problem with GaussView rather than the calculations. – X Zhang Oct 21 '16 at 18:02