some basic questions about atk ( building supercell, optimizing lattice, ...)

[rmbarki]

Hello everybody
I ve just starterd using ATK and it is confusing me  . I am an MD guy and i know that we always need to relax the material and to get the optimized lattice constant, I have a couple of questions:
1- If i need to build my crystal, i know that i can go to database and select my material, but this gives me just a unit cell so how can i create a super cell?
2- Let's say that i want just to find the optimized lattice constant, do i still have to select a calculator in the script manager?
3- Whenever i try to find the optimized lattice constant, i select the material from the data base and then i select a DFT calculator and then i insert optimizegeometry but in the end i get the same initial lattice constant that i specified, am I missing something?
4- i searched in the forum how to relax the material and i found one script, but i didnt know how to use it or more specifically where to copy the script so that the software find it when i call it as a module.

One last comment, i think that it will be good to write a very basic tutorial that explain the main steps to do a simulation. Moreover some pdf files are missing in the website, (403 error page not found)

Any help will be valuable for me.
Thanks 

Raouf

[Nordland]

Hello everybody
I ve just starterd using ATK and it is confusing me  . I am an MD guy and i know that we always need to relax the material and to get the optimized lattice constant, I have a couple of questions:
1- If i need to build my crystal, i know that i can go to database and select my material, but this gives me just a unit cell so how can i create a super cell?

You can drag it into the builder, where you can repeat it to give a super cell, and adjust accordingly with your wishes.

2- Let's say that i want just to find the optimized lattice constant, do i still have to select a calculator in the script manager?

Yes. The lattice constant will to some extended determined by the method, and hence it is needed to make a choice of which method you will use.

3- Whenever i try to find the optimized lattice constant, i select the material from the data base and then i select a DFT calculator and then i insert optimizegeometry but in the end i get the same initial lattice constant that i specified, am I missing something?

By default, the optimization of the cell is disabled, and in order to enable it, you must add the OptimizeGeometry block, and double-click it.
Then untick constraint cell, and now ATK will determine the lattice constant as well.

4- i searched in the forum how to relax the material and i found one script, but i didnt know how to use it or more specifically where to copy the script so that the software find it when i call it as a module.

That script is out-dated since it belongs to ATK 2008.10

One last comment, i think that it will be good to write a very basic tutorial that explain the main steps to do a simulation. Moreover some pdf files are missing in the website, (403 error page not found)

I would recommend the mini-tutorial. http://www.quantumwise.com/publications/tutorials/mini-tutorials

Best regards,
   Nordland

[rmbarki]

Thanks Nordland, so if i have a good understanding, this means that the accuracy of the optimized lattice constant will depend on the selected calculator. I am testing GaAs material and some properties like dielectric and capacitance, do you have any suggestions of a suitable calculator or specific parameters to use here. It is bad that your script is outdated, you dont have any recent version?

Thanks for the clarifications
Raouf

[Nordland]

Yes.

When it comes determining the lattice constant, I would go with the DFT calculator.

I think it is a good idea that my script is outdated, since the feature is now buildin into ATK, and hence it is more stable and better.

[Anders Blom]

Which PDF did you get a 403 or 404 on? (Actually, 403 is forbidden, 404 means missing.)

[rmbarki]

Thanks Nordland for your help so you mean when i use optimizegeometry it uses your script?
Anders, try any pdf file in the section Tutorial and go to the bottom to the section Legacy tutorials for ATK/VNL 2008.10 like for example this link http://quantumwise.com/documents/tutorials/latest/ATK_TutorialSession_Part1_SCF.pdf it is giving me Page not found and all the other pdf also.

[Anders Blom]

Oh the legacy tutorials. Sorry, didn't check those. Thanks, it's fixed now!