What is the best method to calculate the HOMO LUMO GAP in solvent condition and with out solvent condition ?
There are two ways to consider the solvation, through an implicit and explicit method. The first is based on considering the solvation through a conducted-like polarizable method, such as CPCM or universal model (SMD). I think SMD is the best for electronic states. The second is based on adding the solvent molecules around the compound and performing a multilevel QM/MM, where the compound is treated at the quantum-mechanics level and the solvent is treated under molecular mechanics, or even QM/QM with lower level QM for the solvent, such as GFNn-xTB.
In my conception, I think it depends on the information you are trying to extract, but the first is less computationally expansive and considers only the refractive index and the dielectric constant of the solvent. You can use the Gaussian software or Orca to calculate it.
Best wishes.
Thank you for your advice
but my main question was about which method is best
for example at first optimize the molecule with this ( b3lyp/6-31+(d,p) opt scrf(pcm solvent=water)
after optimization complete , convert the out file to the input file with gauss view and then use
b3lyp/6-31+g(d,p) pop=full
for homo lumo gap
or we can use
b3lyp/6-31+g(d,p) opt scrf(pcm solvent=water) pop=full
which one is best?
Got it. It all depends on the system you are modeling because if you are dealing with an organic molecule, the B3LYP/6-31+g(d,p) is ok at best. However, for an inorganic system such as a coordination compound, you have to use a larger basis set. Also, I don't recommend the use of the PCM solvation model, CPCM or SMD are better models.
Here is an example of a robust procedure:
Optimization: B3LYP D4/Def2-SVP for organic molecules, where D4 stands for the dispersion correction, and B3LYP D4/Def2-TZVP for coordination compounds.
Single point: PBE0 D4/Def2-SVP or PBE0 D4/Def2-TZVP.
If you are dealing with excited states, I recommend the use of range-separates hybrid functionals, such as CAM-B3LYP or wB97X.
Thank you sir
yes I’m dealing with organic compound but l didn’t know that’s diffrent for ingorganic compound thank you for sharing your knowledge
Do you have any pdf about basis set in diffrent compund to share with me ? explane about basis set diffrent calculation and...
I think these two papers are very interesting.
Article Efficient Diffuse Basis Sets for Density Functional Theory
Article Best‐Practice DFT Protocols for Basic Molecular Computationa...
thank so much you sir ,
I have another question about temprature
If I want to set my calculation in diffrent temprature and calculate for example gap of homo lumo for organic campound
whats is the formula ?
it is correct ?
b3lyp/6-311++g** pop=full temprature=300(kelvin)
or difrrent temprature ? tempreture=x(kelvin)
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