Is it possible to tell the program to perform calculations for a specific selected number of electrons (only valence electrons, for instance) instead of all electrons to speed up calculations ?
What is the sense behind BSE calculations if GW corrections to the band structures are not provided, or is it possible to provide ELK, GW corrections obtained from another program ?
Bests
Vito
Last edit: vito versace 2015-03-18
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What calculations are you talking about? If you mean ground-state then the answer is No. FP-LAPW is an all electron method. But if you mean BSE calculations then yes. You can choose nvbse (number of valence bands) and ncbse (number of conduction bands), which ristricts the number of Kohn-Sham bands used for calculation and hence number of electrons.
BSE and GW are not two intertwined methoods. GW would correct the ground-state, which in turn can be used to correct the \chi_0. While BSE is a method to calculate fully interacting \chi from what ever ground-state you provide. BSE certainly uses GW approximation for the kernel, but can be used with whatever \chi_0 you choose.
What does GW corrections from other codes mean? If you mean that can you calculate the quasi-particle gap from some code and use that to scissors correct the Kohn-Sham eigenvalues, then yes that can be done. You need to use "scissor" key word in the elk.in
Best
Sangeeta
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Yes, i meant ground-state calculations, i thought that there could be a parameter or something similar to give one the possibility to boost up ground-state calculations, so practically larger unit cells containing heavier atoms are out of reach. I see no reason to calculate small contributions from electrons lying deep in energy, i thought valence and semi core states are much more decisive to obtain physical and reliable results.
BSE also relies on proper GW corrections to the band structure at all k-points as the first term in BSE kernel is a difference between quasi particle energies.
"scissor" : this is a crude approximation and today not necessarily widely used.
Therefore, the calculated peak positions will be unfortunately somehow shifted.
Are LRC-Functionals available in ELK ?
Best
Vito
Last edit: vito versace 2015-03-18
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If you do not want to treat all electrons at the same footing, I suggest you use pseudo potential codes. Vasp and abinit are readily available for this.
As for now, GW is not implemented in the Elk code.
With LRC-functional I take is you mean long range corrected functionals within TDDFT. This is available. Also bootstrap kernel is available with which does not rely on an extrnal parameter like \alpha as required for LRC-kernel.
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Dear all,
Is it possible to tell the program to perform calculations for a specific selected number of electrons (only valence electrons, for instance) instead of all electrons to speed up calculations ?
What is the sense behind BSE calculations if GW corrections to the band structures are not provided, or is it possible to provide ELK, GW corrections obtained from another program ?
Bests
Vito
Last edit: vito versace 2015-03-18
Hi Vito,
What calculations are you talking about? If you mean ground-state then the answer is No. FP-LAPW is an all electron method. But if you mean BSE calculations then yes. You can choose nvbse (number of valence bands) and ncbse (number of conduction bands), which ristricts the number of Kohn-Sham bands used for calculation and hence number of electrons.
BSE and GW are not two intertwined methoods. GW would correct the ground-state, which in turn can be used to correct the \chi_0. While BSE is a method to calculate fully interacting \chi from what ever ground-state you provide. BSE certainly uses GW approximation for the kernel, but can be used with whatever \chi_0 you choose.
What does GW corrections from other codes mean? If you mean that can you calculate the quasi-particle gap from some code and use that to scissors correct the Kohn-Sham eigenvalues, then yes that can be done. You need to use "scissor" key word in the elk.in
Best
Sangeeta
Dear Sharma,
Yes, i meant ground-state calculations, i thought that there could be a parameter or something similar to give one the possibility to boost up ground-state calculations, so practically larger unit cells containing heavier atoms are out of reach. I see no reason to calculate small contributions from electrons lying deep in energy, i thought valence and semi core states are much more decisive to obtain physical and reliable results.
BSE also relies on proper GW corrections to the band structure at all k-points as the first term in BSE kernel is a difference between quasi particle energies.
"scissor" : this is a crude approximation and today not necessarily widely used.
Therefore, the calculated peak positions will be unfortunately somehow shifted.
Are LRC-Functionals available in ELK ?
Best
Vito
Last edit: vito versace 2015-03-18
If you do not want to treat all electrons at the same footing, I suggest you use pseudo potential codes. Vasp and abinit are readily available for this.
As for now, GW is not implemented in the Elk code.
With LRC-functional I take is you mean long range corrected functionals within TDDFT. This is available. Also bootstrap kernel is available with which does not rely on an extrnal parameter like \alpha as required for LRC-kernel.