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General Questions and Answers / Re: Extended Huckel Overlap Element Integration
« on: November 14, 2014, 19:40 »
Just wanted to give this a bump to prevent it from falling off the front page.
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General Questions and Answers / Extended Huckel Overlap Element Integration
« on: November 9, 2014, 02:57 »
Hi,
I'm curious what method (or methods) is used to perform the integration on the two-center integral of the Slater-Type Orbitals (STOs) in the Extended Huckel implementation. STOs are a bit different to integrate, then say, Gaussians. If there are multiple methods, is there a way to control this in ATK?
Thanks.
I'm curious what method (or methods) is used to perform the integration on the two-center integral of the Slater-Type Orbitals (STOs) in the Extended Huckel implementation. STOs are a bit different to integrate, then say, Gaussians. If there are multiple methods, is there a way to control this in ATK?
Thanks.
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General Questions and Answers / Re: Some Extended Huckel questions
« on: June 27, 2014, 06:24 »
1) So just to be sure I understand, you could follow an analagous procedure to find the Fermi level with Huckel that you do with DFT in that tutorial?
3) I've read that portion of the manual pretty thoroughly but I've only glanced through the reference so far. I understood the part about not using parameters in different sources for SCF calculations. What I didn't understand was this:
To first-order non SCF calculations are probably good enough for me right now, but I am curious.
3) I've read that portion of the manual pretty thoroughly but I've only glanced through the reference so far. I understood the part about not using parameters in different sources for SCF calculations. What I didn't understand was this:
Quote
The Hückel parameters have been fitted for non-self-consistent calculations. To use the parameters in self-consistent calculations, the self-consistent onsite shifts must be compensated by a reverse shift of the vacuum_levels.
To first-order non SCF calculations are probably good enough for me right now, but I am curious.
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General Questions and Answers / Re: Some Extended Huckel questions
« on: June 24, 2014, 06:28 »
So I kept looking into my questions and I think I may have made some progress. Perhaps you can tell me if I have gone astray.
I noticed if you export band structure data to text it appears that the E(k) and the Fermi level look to be defined relative to the vacuum. Please correct me if I am wrong here.
Say I am doing an EHT calculation with the Hoffmann parameters where no vacuum energy (Evac) has been set. Suppose I know from experiment that the distance in eV from conduction band minimum (CBM) to vacuum and that is equal to phi. Assuming CBM is measured from vaccuum (again correct me if I'm wrong) then my correct Evac is:
Evac = CBM + phi
Sorry, if I'm being pedantic here, I just want to be painfully clear.
I noticed if you export band structure data to text it appears that the E(k) and the Fermi level look to be defined relative to the vacuum. Please correct me if I am wrong here.
Say I am doing an EHT calculation with the Hoffmann parameters where no vacuum energy (Evac) has been set. Suppose I know from experiment that the distance in eV from conduction band minimum (CBM) to vacuum and that is equal to phi. Assuming CBM is measured from vaccuum (again correct me if I'm wrong) then my correct Evac is:
Evac = CBM + phi
Sorry, if I'm being pedantic here, I just want to be painfully clear.
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General Questions and Answers / Some Extended Huckel questions
« on: June 22, 2014, 19:28 »
Hi,
I'm interested in studying interfaces with ATK's Extended Huckel and while working with it I came up with a few questions.
1.) Not specifically relevant to interfaces, also to bulk calculations or what have you, but how is the Fermi level determined. Say I do a bulk EHT calculation, how is the Fermi level set relative to say, the valence band maxima/conduction band minima?
2.) How exactly is vacuum energy defined? Is it actually the workfunction or is it a shift in the bandstructure to reproduce the correct workfunction? Sorry if this is retreading old ground.
3.) Related question. How to approach band offsets on interfaces? Suppose I know the band offsets from experiment, how should I (or should I) adjust the the vacuum energy? How does that change if I want to use different parameter sets, say Hoffmann parameters for one material (which has no vacuum energy adjustment) and Cerda parameters for another?
Thanks!
I'm interested in studying interfaces with ATK's Extended Huckel and while working with it I came up with a few questions.
1.) Not specifically relevant to interfaces, also to bulk calculations or what have you, but how is the Fermi level determined. Say I do a bulk EHT calculation, how is the Fermi level set relative to say, the valence band maxima/conduction band minima?
2.) How exactly is vacuum energy defined? Is it actually the workfunction or is it a shift in the bandstructure to reproduce the correct workfunction? Sorry if this is retreading old ground.
3.) Related question. How to approach band offsets on interfaces? Suppose I know the band offsets from experiment, how should I (or should I) adjust the the vacuum energy? How does that change if I want to use different parameter sets, say Hoffmann parameters for one material (which has no vacuum energy adjustment) and Cerda parameters for another?
Thanks!
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