Messages

1

General Questions and Answers / Re: Build Hexagonal Closest Packed structure

« on: December 15, 2017, 22:43 »

Hi Petr,

Thank you for the new reply and the useful paper.

I think more about my question/problem.

2

General Questions and Answers / Re: Build Hexagonal Closest Packed structure

« on: December 14, 2017, 22:55 »

Hi Ulrik,

Thank you for the useful suggestion. Indeed we see neighbor cells by choosing repetition in Graphic/properties/cells.
 
However, I would like to know if we could convert or build a conventional cell with 6 atoms/cell (as the link bellows) from a primitive cell of 2 atoms?
http://www.ques10.com/p/9196/draw-the-unit-cell-of-hcp-what-is-the-coordinati-1/

3

General Questions and Answers / Re: Build Hexagonal Closest Packed structure

« on: December 13, 2017, 11:41 »

The repeating option can not help me to create a structure as I desire.

I would like to see a HCP 6 atoms eventually like this:
https://cdn.miniphysics.com/wp-content/uploads/2010/12/HCP.gif
Do you have any other idea?

Thank you.

4

General Questions and Answers / Re: Build Hexagonal Closest Packed structure

« on: December 13, 2017, 10:28 »

Thank you for the reply.
I already have a cif file of the primitive cell of 2 atoms (attached, please remove ".txt" in the file name). To build a HCP structure contains 6 atoms/cell, in the supercell of the builder, how do I change values for A', B', C'?

5

General Questions and Answers / Build Hexagonal Closest Packed structure

« on: December 13, 2017, 00:50 »

Hi all,

I want to build a HCP structure 6 atoms/cell from the primitive cell 2 atoms using the VNL builder. How can I do it? Please advise.

Thank you.

6

General Questions and Answers / Re: Choosing approriate pseudopoptentials

« on: April 3, 2017, 16:02 »

Thank you, Jess Wellendorff.

I am trying to guess a general and an appropriate choice of pseudopotential for this problem, not only with ATK but also with other codes such as Siesta or QE.

7

General Questions and Answers / Choosing approriate pseudopoptentials

« on: April 3, 2017, 10:46 »

Hi all,
In case we have an overlap structure with the middle part made of bilayer structure, and the others made of single layer structure, for instance:
(top layer)            -------------------------------------------

(bottom layer)                                             ------------------------------------------
How should we choose pseudopotentials for DFT calculations?  simply choosing pseudopotentials with GGA, LDA or it should be vdw or even both?



 

8

General Questions and Answers / Re: Why density of states of graphene ribbon with PBC depends on ribbon dimensions?

« on: February 17, 2017, 12:43 »

To make a fair comparison, the DOSs should be divided for number of unit cells  in each calculation (to have DOSs/unit cell) before to compare them

9

General Questions and Answers / Re: hard to remove nagative phonon bands when using classical potential

« on: February 15, 2017, 23:01 »

Dear Petr Khomyakov,

Thank you for taking time to check this problem.

I did try calculations with 2D graphene sheet, but could not remove negative bands even the structure was relaxed (I tried several times).

I will test more, hope I can get luck.

10

General Questions and Answers / Re: Is that ok to do MD relax then put the relaxed coordinate for DFT calculations?

« on: February 15, 2017, 22:50 »

Dear all,
Thank you very much for these fruitful discussions

11

General Questions and Answers / Is that ok to do MD relax then put the relaxed coordinate for DFT calculations?

« on: February 10, 2017, 16:46 »

Dear all,

Relaxation with DFT is usually expensive, particularly for large structures and/or including defects. With vacancy inclusions, many times I can not get relax convergence with QE and Siesta.

So, my question is that: is that ok to do MD relaxation with VNL and then take the relaxed coordinates for other DFT calculations? Is that still safe?

Any ones with experience about this problem, please give comments and advices.

Thank you.

12

General Questions and Answers / hard to remove nagative phonon bands when using classical potential

« on: February 10, 2017, 10:58 »

I re-post my question/concern about phonon bands with classical potential here:

it seems very hard to remove negative bands of graphene if using the potential tersoff_C_2010 (even the structure was optimized). Did you succeed in using this potential?

My concern is that is there any rule when optimizing structures to be sure that negative bands will go away just by one or two times of optimization?

13

General Questions and Answers / Re: negative phonon in phonon band structure

« on: February 3, 2017, 16:28 »

it seems very hard to remove negative bands if using the potential tersoff_C_2010 (even the structure was optimized). Did you succeed in using this potential?

My concern is that is there any rule when optimizing structures to be sure that negative bands will go away just by one or two times of optimization?

14

General Questions and Answers / Viewing the final coordinates of QE relax

« on: February 3, 2017, 13:56 »

Dear VNL developers,

It seems that VNL does not use the final coordinates of relax in QE calculations as I view result relax.out with "viewer". When I selected the file "relax.out" and chose "Text Representation" I saw the coordinates are the initial ones.

I can make a trick by copying the final coordinates into the cif file, so I can view the relaxed structure. However, I expect we can view the relaxed structure directly from the file "relax.out" without further effort. Is that possible to do with the current version of VNL (or QE plugin) or it will be fixed in next versions?


 

15

General Questions and Answers / Re: problem displaying Bandstructure of Graphene: VNL as QE GUI

« on: January 18, 2017, 10:49 »

Thank you, so we wait for your news.