 Re: Total energy in NEGF ( No.1 ) |
- Date: 2015/01/19 17:44
- Name: T. Ozaki
- Hi,
The total energy appearing in the NEGF calculations in OpenMX is calculated based on the
formulation used for the conventional cluster or band methods. Though the theoretical basis
is obscure, one might be able to use the energy to discuss stability of the scattering region
of system from a practical sense. Even the structural optimization might be possible by fixing
position of atoms around the boundaries, as several groups do such calculations, while I have
never checked the issue carefully, however.
Regards,
TO
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| Re: Total energy in NEGF ( No.2 ) |
- Date: 2015/01/26 18:27
- Name: Artem Pulkin <artem.pulkin@epfl.ch>
- Dear Taisuke,
I am working with polar MoS2 and I want to compare the boundary/edge formation energies. Conventionally it is done using 0D structures, see for example here:
http://arxiv.org/pdf/1101.4457.pdf
This approach has a number of drawbacks, mainly due to an unbalanced number of cations and anions in a cluster. I was interested in calculating this kind of energy using NEGF. For example, I create a following symmetric NEGF geometry with identical edges:
| + - | + - | + - | vacuum | - + | - + | - + |
or
| - + | - + | - + | vacuum | + - | + - | + - |
The question is: does the total energy calculated by NEGF includes contribution from a spurious defect coming from connected left and right leads in periodic geometry?
I would like to emphasize that this is not a question about comparing forces or stability. This is a question about comparing 2 different(!) NEGF calculations with right and left leads swapped.
Regards,
Artem
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| Re: Total energy in NEGF ( No.3 ) |
- Date: 2015/01/28 12:02
- Name: T. Ozaki
- Hi,
> The question is: does the total energy calculated by NEGF includes contribution from
> a spurious defect coming from connected left and right leads in periodic geometry?
Do you mean the Coulombic interaction between defects in ......| + - | vacuum | - + |.......
by "contribution from a spurious defect"?
If so, the interaction is actually included in the total energy calculated by NEGF through
the Poisson equation.
Regards,
TO
|
| Re: Total energy in NEGF ( No.4 ) |
- Date: 2015/01/28 18:11
- Name: Artem Pulkin <artem.pulkin@epfl.ch>
- Hi,
I was not clear enough: I mean that there may be some component total energy which is calculated in Fourier space where the scattering region is periodic:
| + - | + - | + - | vacuum | - + | - + | - + | <- spurious interaction -> | + - | + - | + - | vacuum | - + | - + | - + |
I.e. the spurious defect in this case is
| - + | + - |
Of course, I am not a specialist here that's why I ask you if it is the case in OpenMX. If not - good, I will continue to study whether this approach is feasible for polar materials.
Regards,
Artem
|
| Re: Total energy in NEGF ( No.5 ) |
- Date: 2015/01/28 19:20
- Name: T. Ozaki
- Hi,
> | + - | + - | + - | vacuum | - + | - + | - + | <- spurious interaction -> | + - | + - | + - | vacuum | - + | - + | - + |
>
> I.e. the spurious defect in this case is
>
> | - + | + - |
The system treated by NEGF is not periodic along the transport direction, but semi-infinite.
The semi-infinity in evaluating Coulombic interaction is taken into account by solving
the Poisson equation with boundary condition that values of the Hartree potential at
the boundaries between scattering region and leads are fixed at those obtained by
the calculation of the first step. Thus, the interaction "| - + | + - |" is not included
in the NEGF calculation.
Also, the ESM method can be used to eliminate such a spurious interaction
in case of the slab model. The details can be found at
http://www.openmx-square.org/openmx_man3.7/node118.html
and an application can be found in Phys. Rev. B 90, 075422 (2014).
I hope it helps you.
Regards,
TO
|
| Re: Total energy in NEGF ( No.6 ) |
- Date: 2015/01/29 18:56
- Name: Artem Pulkin <artem.pulkin@epfl.ch>
- Thank you, it is a very relevant information.
|
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Total energy in NEGF