I was trying to calculate the ESP in the ground and the 1st excited state (Gaussian 16).
ground state:
POP=chelpg IOp(6/33=2)
excited state:
TD=(Read,Root=1) density=current POP=chelpg IOp(6/33=2)
while I see the differences in the atomic charges in the "out" files, the "cube" files generated are identical in both cases.
What am I doing wrong?
It seems like you are trying to calculate the molecular electrostatic potential (MESP) of a molecule in both its ground and excited state using Gaussian 16. From the input you provided, it looks like you are using the CHELPG scheme to obtain atomic charges and are attempting to visualize the electrostatic potential using cube files.
However, the cube files generated are identical in both cases, which suggests that the excited state MESP is not being computed correctly. To resolve this issue, you can try the following steps:
For the ground state, your input seems to be correct. Here's an example input file for the ground state MESP calculation:
===================================
#P B3LYP/6-31G(d) SCF=Tight Pop=CHelpG IOp(6/33=2) Test
Ground State MESP
0 1
[atom coordinates]
===================================
For the excited state, you should separately calculate the excited state density using the TD-DFT method and generate a checkpoint file (.chk). Then, use the checkpoint file to compute the MESP for the excited state. Here's an example input file for the excited state MESP calculation:
===================================
#P B3LYP/6-31G(d) TD=(Read,Root=1) SCF=Tight Test
Excited State MESP - Step 1
0 1
[atom coordinates]
--Link1--
%Chk=filename.chk
#P B3LYP/6-31G(d) Geom=AllCheck Guess=(Read,Only) Density=(Check,Transition=1) Pop=CHelpG IOp(6/33=2) Test
Excited State MESP - Step 2
===================================
Replace [atom coordinates] with your molecular geometry. Make sure to use the same method and basis set for both ground and excited state calculations.
These changes should give you different cube files for the ground and excited states, and you should be able to visualize the differences in MESP using visualization software like VMD or GaussView.
Regards,
Dear Alessandro Rizzo,
Thank you very much for the answer,
I've just tried your approach and it doesn't work.
Maybe I've done something wrong and I simply do not see it, so, please, take a look at my complete inputs:
GROUND STATE:
%oldchk=f_.chk
%chk=f_MEP_G0S0.chk
# wb97xd/6-311++g(d,p) POP=chelpg IOp(6/33=2) output=wfn geom=allcheck scf=(tight,maxcycle=999)
f_MEP_G0S0.wfn
EXCITED STATE 1ST STEP:
%oldchk=f_TD.chk
%chk=f_MEP_G0S1_prep.chk
# TD=(Read,Root=1) wb97xd/6-311++g(d,p) geom=allcheck integral=grid=finegrid scf=(tight,maxcycle=999)
EXCITED STATE 2ND STEP:
%oldchk=f_MEP_G0S1_prep.chk
%chk=f_MEP_G0S1.chk
# wb97xd/6-311++g(d,p) POP=chelpg IOp(6/33=2) density=(Check,Transition=1) output=wfn geom=allcheck guess=(read,only) integral=grid=finegrid scf=(tight,maxcycle=999)
f_MEP_G0S1.wfn
I've also tested this approach for POP=NBO (without IOp(6/33=2) option) and the obtained NBO charges for all the atoms are exactly the same in the ground and excited state.
Best regards,
Radek
Dear Radek,
Thank you for providing your input files. I see that you are trying to calculate the MESP for the ground and the first excited state using the wb97xd functional with the 6-311++g(d,p) basis set. It appears you are using a two-step process for the excited state calculation.
Based on the input files you provided, I have a few suggestions that you might want to try:
step.1 : In the first excited state step, include the "IOp(5/32=2)" option, which will store the transition density matrix in the checkpoint file. Modify your input as follows:
==============================================
EXCITED STATE 1ST STEP:
%oldchk=f_TD.chk
%chk=f_MEP_G0S1_prep.chk
# TD=(Read,Root=1) wb97xd/6-311++g(d,p) geom=allcheck integral=grid=finegrid scf=(tight,maxcycle=999) IOp(5/32=2)
==============================================
step.2 : In the second excited state step, use the "Density=(Check,Transition=1)" option to read the transition density matrix from the checkpoint file. Modify your input as follows:
==============================================
EXCITED STATE 2ND STEP:
%oldchk=f_MEP_G0S1_prep.chk
%chk=f_MEP_G0S1.chk
# wb97xd/6-311++g(d,p) POP=chelpg IOp(6/33=2) density=(Check,Transition=1) output=wfn geom=allcheck guess=(read,only) integral=grid=finegrid scf=(tight,maxcycle=999)
f_MEP_G0S1.wfn
==============================================
By implementing these changes, you should be able to compute the molecular electrostatic potential (MESP) for both the ground and the first excited state using Gaussian 16.
Please try these modifications in your input files and let me know if you encounter any issues.
Regards
Alessandro
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