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Given that Kohn-Sham DFT is strictly a ground-state method (at 0 K), how is it sufficient to describe materials in real-life applications?

These are a few extra points to complement Andrew Rosen's comprehensive response: To be absolutely clear, typical DFT calculations are not performed at 0K, a better description of what happens is ...
ProfM's user avatar
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22 votes

Given that Kohn-Sham DFT is strictly a ground-state method (at 0 K), how is it sufficient to describe materials in real-life applications?

You are correct that KS-DFT, strictly speaking, involves calculations of a potential energy surface at 0 K. However, if you accept that the density functional approximation you are using is ...
Andrew Rosen's user avatar
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20 votes

What are the types of DFT?

CDFT: Current DFT Current DFT is defined via the generalized Hohenberg-Kohn theorem (HKT), which extends the traditional HKT to account for the effect of magnetic fields. The generalized HKT says that ...
Tyberius's user avatar
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19 votes

What are the types of DFT?

OF-DFT: Orbital-free density functional theory Hohenberg and Kohn established that the ground state energy, $E$, of interacting electrons in a potential, $v(\mathbf{r})$, is a functional of the ...
wcw's user avatar
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13 votes
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What methods are available for excited state calculations in solids?

$\Delta$SCF This method generates excited states by changing the occupancy of a ground state determinant and then carrying out a new SCF with that initial guess, with some restriction throughout to ...
Tyberius's user avatar
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12 votes

Given that Kohn-Sham DFT is strictly a ground-state method (at 0 K), how is it sufficient to describe materials in real-life applications?

Kohn-Sham DFT may only be rigorous at zero temperature, but at nonzero temperature, Kohn-Sham-Mermin DFT is an equally rigorous replacement. There are two major differences Rather than deriving the ...
Endulum's user avatar
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11 votes
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Is it possible to do TD-DFT/6-31G+(d,p) calculations on a laptop?

Basis set name versus number of total orbitals I would like to first address a part of the question that appears to be a misconception about the use of a 6-31+G(d,p) basis set, since you wrote: "...
Nike Dattani's user avatar
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10 votes

What methods are available for excited state calculations in solids?

GW+BSE: Excited states in the framework of many-body Green's function comprise charged excitations, where the number of electrons in the system changes from $N$ to $N-1$ or $N + 1$, and natural ...
Jack's user avatar
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10 votes
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How can reactivity indices be calculated in a time-dependent scheme?

Time-evolution of conceptual DFT quantities has been considered starting, I think, with Chattaraj ~2000. (I imagine there is some earlier work by Ghosh and/or Harbola, but I do not know a reference.) ...
Paul Ayers's user avatar
10 votes

What are the types of DFT?

KS-DFT: Kohn-Sham DFT The KS-DFT is proposed to deal with the problems of orbital-free DFT (OFDFT), which has been explained by @wcw. OFDFT attempts to compute the energy of interacting electrons, as ...
Jack's user avatar
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10 votes

What are the types of DFT?

Density functional perturbation theory (DFPT) This method refers to the calculation of the linear response of the system under some external perturbation. Consider some set of parameters $\{\lambda_i\}...
ProfM's user avatar
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10 votes
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Different types of transition dipole moment in ORCA output

You have stumbled across a problem that was described in 1983 in the following way (note that the "40 years" refers to 1943-1983): "Over the past 40 years, many authors have tried to ...
Nike Dattani's user avatar
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9 votes
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What are the types of DFT?

Real-time TDDFT (RT-TDDFT) This is the straightforward non-perturbative solution of the TDDFT equations by means of direct propagation in time. Pioneered by Theilhaber and Yabana & Bertsch it has ...
LukasK's user avatar
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9 votes

Is it reasonable to calculate TDDFT excitation energies at a geometry optimized with a different method?

From my point of view, it will not affect so much on the excitation energy, but it is preferred to use the same level of functional and basis set unless you will increase the level of theory to get ...
Abd-Elazeem Mohamed's user avatar
8 votes
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Is there a software that has implemented forces of BSE calculations for solids?

I am not aware of any public codes that have a force implementation for excited state calculations using the Bethe-Salpeter equation (happy to be corrected on this front). However, the methodology to ...
ProfM's user avatar
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8 votes
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How do you calculate the change in dipole moment from ground to first excited state using ORCA?

This second dipole moment is almost surely the excited state. You can see the nuclear contributions are identical and the rotational constants are also the same. This means they are both ...
Tristan Maxson's user avatar
8 votes

What are the recent developments of GW@BSE to simulate the excited properties of materials?

As one of the members of the Yambo group I can answer for the developments, in the Yambo code, in particular related to GW and BSE. One important aspect is the code optimization, and the connected ...
Davide Sangalli's user avatar
8 votes

Understanding emission spectra using TDDFT calculation

In general, you should use the $S_1$ state by default, unless you have reasons to suspect that your molecule is anti-Kasha. IMHO satisfying one of the following criteria guarantees that your molecule ...
wzkchem5's user avatar
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8 votes

Validity of adiabatic approximation in TDDFT

The time scale is related to time derivative of the kinetic energy of electrons defined as: $$T(t) = \sum_{i} \int |\nabla \phi_{i}(\mathbf{r},t)|^{2} d^{3} \mathbf{r}$$ You have this for time-...
Mithridates the Great's user avatar
8 votes
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Regarding oscillatory strength theoretical units to experimental ones

The expression you are describing is equation (6) from your first link: $$R_j=\frac{3\hbar c\ln(10)1000}{16\pi^2N_A}\int_\text{band j}\frac{\Delta\epsilon}{\omega}d\omega\tag{1}$$ which defines the ...
Tyberius's user avatar
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7 votes
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Is there an example where TD-DFT fails to provide sufficient accuracy for a small system, where RI-CC2 is sufficient?

The question cites a 2008 paper about fairly large molecules (e.g. bithiophene N-succinimidyl esters), in which TD-DFT gave significantly wrong results, so the authors recommended RI-CC2. The question ...
Nike Dattani's user avatar
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7 votes
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Deviation caused by using DFT in Non-Adiabatic Molecular Dynamics

"But since the DFT works not so well when dealing with semiconductors and excited-state calculations, wouldn't NAMD be too erroneous considering the nuclei vibrations?" First of all, DFT in ...
Nike Dattani's user avatar
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7 votes
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Is it reasonable to calculate TDDFT excitation energies at a geometry optimized with a different method?

The question, in some sense, is "how accurate is the geometry?" Yes, in principal, you should do TD-DFT on a true minimum geometry. However, the diagram also indicates that if you displace ...
Geoff Hutchison's user avatar
7 votes

Any software that could do surface hopping?

Here are some options. Depending on what you want you may use on-the-fly electronic structure calculations for energies, gradients, and couplings and some of the codes can take care of integrating the ...
Antonio de Oliveira-Filho's user avatar
7 votes

Vertical transition, 0-0 transition, and experimental spectra

Yes, the absorption maximum is usually close to (but not necessarily exactly equal to) the vertical excitation from the ground state, due to the Franck-Condon principle. However, this does not mean ...
wzkchem5's user avatar
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7 votes
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S1-T1 energy difference in Gaussian

The excitation energies are 3.09 and 2.17 eV, respectively, both relative to the (same) ground state, and thus the energy difference is 3.09 - 2.17 = 0.92 eV. The Total Energy is the ground state ...
Frank Jensen's user avatar
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6 votes

What is the importance of electron interaction on dielectric response of crystals?

I think you should take care of all possible interactions to get close to the real picture. In periodic solids, there might be electron-hole interaction (solve BSE equation for it), el-phonon coupling,...
Haseeb Ahmad's user avatar
6 votes

Different types of transition dipole moment in ORCA output

To give a little background on where these different forms come from, it is related to gauge theory in electromagnetism. We can represent an electromagnetic field through Maxwell's equations using a ...
Tyberius's user avatar
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6 votes

Any software that could do surface hopping?

Newton-X Newton-X is a general program for molecular dynamics simulations beyond the Born-Oppenheimer approximation. It has been primarily used for simulations of ultrafast processes (femtosecond to ...
Felix's user avatar
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6 votes
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how can I distiguish between pi-pi* or n-pi* while doing a TDDFT calculus on gaussian?

There are a few methods, that are equivalent as long as the excited state is either an almost pure pi-pi* state or an almost pure n-pi* state (i.e. no appreciable mixings between these two types of ...
wzkchem5's user avatar
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