# Tag Info

12

Time-dependent DFT can be used to predict excitation energies through a linear-response formulation. In this Gaussian result, beyond the first line, you are looking at the largest coefficients in the configuration-interaction (CI) style expansion. (It's not strictly CI, but the implementation of time-dependent HF or RPA is essentially the same for TDDFT or ...

8

What is sometimes done is use the geometry and thermochemical corrections (i.e. the results of the frequency calculation) of method X, but use the electronic energy (SCF energy) of another method Y. This is generally noted Y//X. Since the geometries and thermochemical corrections typically are not much influenced by the quality of the method (beyond a ...

8

To visualise the orbitals of your calculation, use a program of your choice. For Gamess, there are a few options availabile. I use ChemCraft and Molden, and they work quite well. Here is a compilation of some with the former mentioned: You can further use the summary to identify the most interesting, strongest transitions: SUMMARY ...

8

Conventional density functional theory (DFT) is strictly limited to describing the electronic density of ground electronic states. This is because the Hohenberg–Kohn theorems, on which it is based, are restricted to non-degenerate ground states (with no magnetic field). Also, because DFT aims at solving the time-independent Schrödinger equation (i.e. it ...

7

There is a related discussion on which method to use for a singlet triplet guess, which I encourage you to also read: U- or RO-method for Singlet-Triplet Gap? This post is going to be a little longer, so I'll present the key points upfront. It is reasonable to calculate (and/or optimise) the wave function with a restricted method, then test it for ...

7

By definition, the transition density is not the same as the difference density. In the following derivation, the transition density is $\mathbf{T}^{\mathrm{CIS}}$ and the difference density is $\mathbf{P}^{\Delta}$. Although it may seem like they can be formed from the same quantities, the true difference density contains orbital relaxation terms and can be ...

6

Yes it is very common particularly in the more rigid type of molecule. The best example is chlorophyll and this overlap of absorption and emission leads to energy transfer in photosynthesis. The reason for the overlap is that the excited state potential energy profile is very similar in shape but slightly shifted (as displacement) to that of the ground ...

5

When you can, use TDDFT, in part because of the oscillator strengths I like to point out to my group that optical excitations consist of two things consistently (e.g., in a UV/Vis spectra). There are the excitation energies (the x-axis) and the intensity or extinction coefficient (the y-axis). To some degree, the peak widths give a bit more information (e.g....

4

You are looking at the wrong numbers. You should look for excitation that has non-zero oscillator strength. In the text file "State # 1,2 .." and in Chemissian on the left, list with columns "# Energy Strength" The transitions with zero or very small oscillator strength has a very low intensity in the spectrum, so you don't see them. In your case the ...

3

Form this output you dont. Find this in the output: EXCITATION DE-EXCITATION OCC VIR AMPLITUDE AMPLITUDE I A X(I->A) Y(A->I) --- --- -------- -------- 10 17 -0.039945 0.001926 16 17 0.996619 -0.032612 16 20 -0.070681 0.003443 it shows you the involved ...

3

First if all, I appreciate you and thank you for putting up such a good question. One thing I will request you to note here is the definition of temperature. Temperature, in broad sense, is defined as the average kinetic energy (for equilibrium conditions, I hope you are speaking of that) of a system. The contribution mostly arises from translational ...

2

Temperature is difficult to capture in any electronic structure theory (not just DFT) because almost all of them invoke the Born-Oppenheimer approximation. The BO approximation assumes the electrons instantaneously equilibrate to the current nuclear configuration (geometry). The difficulty arises then because most theories assume the nuclei are stationary as ...

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