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25 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 ...
  • 10.4k
20 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 ...
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12 votes
Accepted

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 ...
  • 14.3k
11 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 ...
  • 211
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 ...
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9 votes
Accepted

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 ...
8 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 ...
8 votes
Accepted

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. ...
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 ...
  • 10.4k
8 votes
Accepted

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 ...
  • 29.1k
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 ...
  • 10.4k
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 ...
  • 7,463
4 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 ...
  • 14k
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/...
  • 14k
3 votes
Accepted

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 ...
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.
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 ...
  • 14k

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