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solan

Member

Registered: 2024-04-02

Posts: 12

Double states

First of all, I would like to express my appreciation for your versatile and useful program. I am currently performing calculations on Trityl (triphenylmethyl) radicals, which are doublet ground-state systems. When computing their excited states using TD-DFT in Gaussian, how can I identify the corresponding D₁ and D₂ energies? Are they simply the first two states listed in the output?

I notice that both states have very similar energies, with a difference of only about 0.01 nm, which seems somewhat counterintuitive to me.

Thank you very much in advance for your assistance.

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 2,111

Website

Re: Double states

You need to check <S**2>, if an excited state can be regarded as a doublet state, its <S**2> should be close to 0.75 (for example, 0.82 is acceptable, but 1.01 cannot be regarded as doublet, indicating it has significantly spin contamination)

solan

Member

Registered: 2024-04-02

Posts: 12

Re: Double states

Thank you very much for your quick and insightful response; it has made the concept much clearer to me, and I will investigate it in more depth. Likewise, which functional would be suitable for studying this type of radical? I have seen that many people use B3LYP directly, but that seems to be a convenient choice rather than the result of a methodical study. Would ωB97X-D be appropriate?

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 2,111

Website

Re: Double states

It you focus on local excitation, B3LYP or PBE0 is a reasonable choice. If there are charge-transfer excitations, wB97XD or CAM-B3LYP would be better for them (but they often overestimate excitation energy of local excitations)

solan

Member

Registered: 2024-04-02

Posts: 12

Re: Double states

Thank you very much !!