TD DFT - BNNLab/BN_Group_Wiki GitHub Wiki
Calculating the redox potential of a compound using Gaussian involves setting up an input file for a TD-DFT (Time-Dependent Density Functional Theory) calculation. Let’s create an example input file step by step:
Geometry Optimization: First, optimize the molecular geometry of your compound using DFT. Suppose you have already optimized the structure and verified it as a minimum. Here’s an example input file for the optimization step:
%Chk=tddft
# B3LYP/6-311+G(2d,p) Opt
Title
0 1
C 0.000000 0.000000 0.000000
H 1.089000 0.000000 0.000000
H -0.363000 1.029000 0.000000
H -0.363000 -1.029000 0.000000
In this example:
We use the B3LYP functional with the 6-311+G(2d,p) basis set for optimization.
The molecule has a neutral charge (0) and a singlet spin state (1).
TD-DFT Calculation: Next, perform a TD-DFT calculation to obtain excited states. Save the checkpoint file from the optimization step. Here’s an example input file for the TD-DFT calculation (let’s assume we’re interested in the third excited state):
%OldChk=tddft
%Chk=state3
# B3LYP/6-311+G(2d,p) Geom=AllCheck Guess=(Read,Only) Density=(Check,Transition=3) TD(NStates=40)
Title
The %OldChk=tddft
line specifies the checkpoint file from the optimization.
We compute the NTOs (Natural Transition Orbitals) for the third excited state.
The Pop=(Minimal,NTO,SaveNTO)
option generates NTOs and replaces the ground state orbitals in the checkpoint file.
Analyze the Output: The Gaussian output file (outputfile.out) will contain information about the redox potential, energies, optimized geometry, vibrational frequencies, and electronic properties. Pay attention to the total energy and ensure convergence with the chosen level of theory and basis set.
Remember that this is a simplified example, and you should adapt it to your specific compound and research needs. Happy calculating! 🌟
For more details, consult the Gaussian reference manual and tutorials12.
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