Dear all:
I’m working on a project where I use ESP charges from ground and excited states. I’ve encountered a confusion when using TDDFT (with CAM-B3LYP) for analyzing ground-state charges — yes, I know TDDFT is intended for excited states, but I’ll explain why I’m asking.
My system consists of a polymer of 122 atoms, and I need two set of charges:
- DFT-ESP ground state charges.
- TDDFT - ESP excited state charges.
However, when I get the results from DFT, I get odd charges, like -17 for a carbon atom, and then another carbon atom of 16. Then, when I compute the charges for the excited state using the next input:
BASIS = 6-31+G*
CIS_CONVERGENCE = 6
CIS_N_ROOTS = 5
CIS_TRIPLETS = FALSE
CIS_RELAXED_DENSITY = TRUE
RPA = 0
GUI = 2
ESP_CHARGES = 1
METHOD = CAMB3LYP
One I had the output from the TDDFT, I realized that it also included a list of ground state ESP charges before the set of charges for excited states, and those didn’t match at all with the DFT ESP charges. In fact, those from the TDDFT calculation made more sense than DFT.
I then compared the approach by getting the same set of charges for a smaller molecule, and this time, the charges in ground state from DFT and TDDFT matched exactly.
Has anyone worked with this kind of set up before? Do you know why this might be happening?
Thanks for your help,
Samantha.