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29 votes
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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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23 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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13 votes
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KS-DFT versus G0W0

I am going to try to go systematically through your question and answer the critical bits. I may edit this answer going forward as I'm able to express my thoughts better or people point out important ...
Anubhab Haldar's user avatar
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
  • 221
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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9 votes
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VASP GW PAW Pseudopotentials

A lot of it will be in the difference in cost. But as a rule of thumb, GW potentials are typically harder, and include more states (semicores). This need not always be the case, since if you look at ...
Anubhab Haldar's user avatar
8 votes
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Can GW-BSE quasiparticle calculations only be run on norm-conserving pseudopotentials (NCPPs)? If so, why not?

The GPAW code can do GW/BSE and it uses purely PAW potentials. So it's absolutely possible to do GW/BSE with PAW sets. The involvement for the implementation, however, is another topic. From Kevin J. ...
Anubhab Haldar'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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What's the meaning of absorbance in the absorption spectrum calculated by the GW-BSE method?

The term absorbance does not have anything directly related to the GW approximation or the Bethe-Salpeter equation (BSE). The "absorbance" is a property of a material, while GW and BSE are ...
Nike Dattani - No Free Time'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
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Which strategy of improving the DFT band gap is the most effective?

It's a nice question, it will be difficult to compare their accuracy and efficiency in a single plot, because the band gap problem is mainly divided into two parts: the self-interaction and the ...
M06-2x's user avatar
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7 votes

Density Functional Perturbation Theory

Density functional perturbation theory is a way to calculate the response of a system to some perturbation. For example, you can use DFPT to calculate the response due to small displacements of atoms (...
AGS's user avatar
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7 votes

How to evaluate the exciton velocity?

Not a direct answer to your proposed approximation to the exciton group velocity as $\mathbf{Q}\to0$, but just wanted to point out that the latest version of Yambo supports the calculation of exciton ...
ProfM's user avatar
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6 votes

Recommended code to do XAS/XES/RIXS calculations with?

The computational chemistry software ORCA (requires the registration of an account, although both registration and the software itself is free for academic users; for a tutorial that is viewable ...
wzkchem5's user avatar
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5 votes

VASP GW+SOC band structure calculations

Here I show the typical calculation flow of GW in VASP: a DFT ground-state calculation. obtain DFT virtual orbitals GW calculation including LWANNIER90 TAG Compute Wannier functions and Obtain ...
Jack's user avatar
  • 15.2k
5 votes

What are the recent developments of TDDFT to simulate the excited properties of materials?

Time-dependent density functional theory (TDDFT) has indeed seen significant developments since its review in the classical paper you mentioned. One of the recent advancements in TDDFT is: Nonlinear ...
Jaafar Mehrez's user avatar
5 votes

Density Functional Perturbation Theory

To amend AGS's answer, in density functional perturbation theory one looks at how small perturbations to the system affect properties such as dipole moments, excitation energies, etc. Many-body ...
Susi Lehtola's user avatar
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4 votes
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Is the HOMO energy obtained from GW calculation always a value relative to the vacuum energy (-Ip)?

In the meantime, Daniele Varsano answered me on the Yambo forum. I quote him below: In Yambo, the zero of the energy is set at the valence band maximum (VBM). The GW will give you the correction to ...
3 votes

BSE and IQP oscillator strength from VASP

Your question is not so focus. I assume that you want to read the BSE oscillator strength from the VASP output. I strongly advise you that take a look at this link: https://www.vasp.at/wiki/index.php/...
Jack's user avatar
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2 votes
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How to plot absorbance from a Quantum ESPRESSO optical calculation using ε1, ε2, and energy data?

What you have done so far is that you now have calculated the real and the imaginary parts of the dielectric functions, which is a function of $\omega$, i.e., $Re(\varepsilon(\omega)) = \varepsilon_1(...
Abdul Muhaymin -Free Palestine's user avatar
2 votes
Accepted

How to plot exciton wave function with phase information?

Found a small script for BGW to do the plot https://github.com/BerkeleyGW/bgwtools/blob/master/bgwtools/BSE/plot_envelope.py.
Xiaoming Wang's user avatar
2 votes

How to plot exciton wave function with phase information?

I think these figures are plotting the square of $A_{vc\vec{k}}$, therefore no phase information is contained in these figures. Note that the figures that you are showing are marking each excitonic ...
Jack's user avatar
  • 15.2k
2 votes

Recommended code to do XAS/XES/RIXS calculations with?

Adding to wzkchem5's answer, you might also consider using Quanty. The program is a many body script language based on Lua that allows you to calculate XAS, NIXS and RIXS spectra, among other things. ...
manju9's user avatar
  • 248

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