Specifically, for HOMO, LUMO, energy gap (ΔE) and molecular electrostatic potential calculations, what are the actual methods in DFT? Can I get it through optimized file or need anything else.
As a theory expart what will you do for these parameters.
Dear Nayim Sepay ,
HOMO, LUMO are readily available through computational calculations. Concerning functionals to use if you perform DFT, you have many, more or less adapted to situations (NMR, transition-state etc ...). If your objective is only to know the energy of these orbitals and their shapes, B3LYP or M062X should be appropriate. You could then calculate the energy gap ∆E easily.
If you want to study excited-states of your molecule, ∆E is not often a good criterion. You should perform TD-DFT calculation (if you want to continue on working with DFT) on your molecule to determine the excitation energies.
Concerning molecular electrostatic potential, it is very to obtain and plot. If you are a Gaussian user, just ask the program to write a *.chk file (checkpoint). Then, with the command 'formchk' you can convert your *.chk file to a *.fchk file (formatted checkpoint). Then, the utility "cubegen" will help you to create *.cube file containing either the information of electron density or electrostatic potential. As en example: cubegen 0 density=SCF my_molecule.fchk my_molecule-dens.cube.
There are many options with this utility and it is well described in the documentation of Gaussian.
Directly from the *.fchk file you could use Multiwfn (free) which can perform a lot of useful calculations.
If you don't have Gaussian, Orca is free and is able to do the same calculations.
If you are using small molecules then Firefly or GAMESS can be used to predict HOMO, LUMO, band gap etc.Firefly has a GUI. Input the molecule as z matrix or coordinate -select your basis set and RHF/ROHF/UHF as you need-add MP correlation if you want to calculate correlation energy-Run the programme using Firefly GUI- in the results search for molecular orbitals-the highest negative orbital is HOMO and the lowest positive orbital is LUMO. Energy gap can also be obtained from the GUI directly.
Also you may want to go beyond DFT, e.g. by using ab initio methods like CCSD(T), or in the context of DFT: GW. qsGW performs rather well:
https://www.scm.com/highlights/fast-and-accurate-ionization-potentials-and-electron-affinities-with-qsgw/
Thank you very much Corentin Lefebvre , Aby Jimson , and T. P M Goumans for your kind answer.
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