Messages

1

General Questions and Answers / Re: LCAO basis set used for initialisation and projection in PlaneWave caclulator

« on: August 11, 2020, 08:44 »

Hi hsuya,

An DFT code (LCAO or Plane-Wave) need a initial guess for the electron density. The plane wave code uses LCAO orbitals to create a starting density for the self-consistent loop. This is what is meant by initialiation.

In addition, some post-analysis of the self-consistent state requires a projection onto atomic orbitals, and here the LCAO orbtials are used again.

2

Installation and License Questions / Re: Cannot access from other users

« on: June 30, 2020, 08:16 »

Normally this would depend on the file permission controled by the HPCC admin.

What are the permission of the installation files? and what error are you seeing?

3

General Questions and Answers / Re: Can not repeat the result of piezoelectric coefficients of example GaAs

« on: June 4, 2020, 08:39 »

Are you running the exact same script from the manual?

4

General Questions and Answers / Re: modelling of metal ions adsorption on graphene sheet

« on: June 4, 2020, 08:38 »

There is a simulation choice you have to make, and there is pro's and con's depending on how you do it.

If I were to carry out the simulation, I would add the total charge to the system. This is for me the least 'biased' simulation of the system.

5

General Questions and Answers / Re: ATK vs VASP benchmarks

« on: June 4, 2020, 08:34 »

As a rule of thumb and of course, somewhat anecdotal, LCAO performs best for large and complex structures, where PW solutions perform best for smaller systems.

6

General Questions and Answers / Re: Performing physisorption

« on: February 27, 2020, 15:07 »

From an ab-initio simulation point of view, it would be the same calculation.

Hand-waving we would call reaction with a low energy gain for physisorption and those with a high energy gain for chemisorption.

Another way to quantify it would be to look at the molecular levels of the molecule alone versus the molecule on the surface.
According to Wikipedia:
Physisorption, also called physical adsorption, is a process in which the electronic structure of the atom or molecule is barely perturbed upon adsorption.

Therefore if you compare the molecular spectrum of both cases, and they are similar, you could classify it as physisorption. If they are significantly changed,  then you could classify it as chemisorption

7

General Questions and Answers / Re: Incorporating Van der waal forces

« on: February 27, 2020, 14:57 »

You can choose to use the DFT-D2 forces in geometry or only add it afterwards. I would recommend keeping a consistent model and use DFT-D2 all the way if you want to study the effect of Van der waal forces.

8

General Questions and Answers / Re: Boundary Conditions

« on: February 27, 2020, 14:54 »

You should pick Dirichlet or Neumann.

9

General Questions and Answers / Re: Passivation with elements other than Hydrogen

« on: August 14, 2017, 14:50 »

One trick that could bring you a part of the way, is that if you use the Custom Passivator, all atoms that you add will get a tag, and if you then use the selection tool (Tag) you can select all of thoses atoms with a single click and replace them with your choice of element.

10

General Questions and Answers / Re: Implementation change of the TB09 functional

« on: May 2, 2016, 19:34 »

Hey Fuchs.

There is a set of minor changes to make it more precise that has been implemented. The old result should still be valid, but an old c-parameter would have to be reevaluate to give new consistent results. There are one important changes that is the most likely cause of the different that you see.

• The MGGA contains the kinetic energy density which is straight forward to calculate for the  valence density (since we know the wave function), but for the nonlinear core correction which comes from the pseudo-potential we only have a density and hence there is no direct way to calculate the kinetic energy density for this. We tested various approximation for kinetic energy density for this nonlinear core-correction and picked the approximation that gave the best results.

11

General Questions and Answers / Re: One probe systems

« on: October 26, 2015, 15:15 »

Hey asanchez.

There is indeed one-probe support in the 2015.0 version, however it is not really supported in the VNL.
It can be viewed in the Viewer and most results can be visualized using the normal tools.

I have attached a small example script on how to define the structure (which is called a SurfaceConfiguration),
and a screenshot of it in Viewer. We are getting some real exiting result from this feature, so any feedback is very welcome.

Best regards,
   Søren

12

Installation and License Questions / Re: vnl.exe does not open after installation on Intel Xeon

« on: September 18, 2015, 09:43 »

Have you installed the 32bit or the 64bit version and what is your operating system running 32bit or 64bit?

13

General Questions and Answers / Re: Optical spectra e-h interaction

« on: July 13, 2015, 10:50 »

It is the single particle states that are used for the optical spectrum, so it does not include exciton effects.

14

General Questions and Answers / Re: increased number steps-does not work to overcome convergence proble

« on: May 11, 2015, 09:43 »

Try increasing the electrode temperature.

15

General Questions and Answers / Re: default k-points integration methods?

« on: March 2, 2015, 23:56 »

Dear ATK team,

Hey!

Based on my knowledge, there will be k-point integration (as gaussian smearing or tetrahedron methods) in every SCF steps in periodic system calculation.

In each step in SCF, the Hamiltonian is calculated for a set of different fourier components given by your k-points in your Monkhorst-Pack grid. In ATK the Hamiltonian is
represented  in a real space representation, so you will only need enough fourier components to make this Hamiltonian converged.
This is usually a few number of k-points needed to obtain this.

When we calculate DOS by different k-point integration schemes (gaussian smearing or tetrahedron method), we can use .nc file  of the previous SCF results.
I think if DOS by certain k-point integration scheme should be meaningful, the SCF calculations also performed by the same integration scheme.

This comes down to what you mean with meaningful. Since ATK uses a real space Hamiltonian, it is possible to calculate any fourier component from this,
as a post-process. If the real space Hamiltonian is converged in terms of k-points, this is an exact operation - and the DOS can then be calculated as correct for
any new k-points that might not have been in the SCF part.