Messages

1

General Questions and Answers / LDOS script help

« on: June 21, 2012, 04:36 »

Hi,

I'm currently running some STM/STS experiments, and want to generate some LDOS plots to compare to my dI/dV. I know dI/dV and LDOS aren't equal to one another, but there is a correlation.

I've put together a device system with the surface I'm interested in, and will be creating vacancies and defects in the surface structure, followed by a geometry optimisation, then calculating the LDOS. I've run a couple of LDOS calculations and it seems to be working, but now I want to cut out quite a bit of the work. Is there a script I can use which will run the LDOS calculation over a range of energies, so I can start just one calculation which will cover my range of interest, rather than having to initiate ~20 calculations, one after the other?

I've seen that there is a way to extract the LDOS at a particular grid point; how do I find the coordinates of the grid point(s) I am interested in so that I can add a script to extract just these values (as I only want to know the LDOS at the defect I induce), and can the fact that I am only interested in a few specific points be used to speed up the calculation in any way? I suspect the answer to this question will be no, due to the self consistent nature of DFT calculations, but I thought I would check.

Thanks very much

2

General Questions and Answers / Surface electron affinity

« on: December 7, 2011, 23:43 »

Hi,

I want to calculate the electron affinity of a surface. I know that there is a tutorial which shows how to do this for a single molecule, but is the process the same for a surface?

Thanks

3

General Questions and Answers / Re: zone folding

« on: November 21, 2011, 08:13 »

Thanks. Looks like some pretty heavy coding to get that working, I might give it a few months before I try

4

General Questions and Answers / zone folding

« on: November 21, 2011, 05:25 »

Hi,
How can I remove the effects of zone folding on my calculated band structures? I've done some simple calculations on the database model of graphene, but now I want to repeat these calculations on a larger cell of graphene. Ultimately I want to put molecules on top of the graphene layer and look at the change in bandstructure due to the presence of the molecules, for which I need a larger graphene unit cell.
Thanks

5

General Questions and Answers / Re: different basis sets for same-type atoms

« on: November 21, 2011, 00:50 »

Brilliant, thank you. That's exactly what I need, and for much the same reason-I want higher basis sets than my surface atoms than for the bulk. Now I can finally get this calculation working properly

6

General Questions and Answers / different basis sets for same-type atoms

« on: November 20, 2011, 12:53 »

Hi,
Is there any way to modify a script so that different basis sets are used for specific atoms? I know that the GUI allows the easy application of different basis sets to different elements in a structure, I want to take this one step further and apply different basis sets to specific atoms of the same element.
Thanks

7

General Questions and Answers / Re: Surface geometry optimisation

« on: November 15, 2011, 08:05 »

Thanks-too many late nights lately, I hadn't thought of nudging the surface atoms in case there is an energy minimum, most of your other suggestions I had already considered. I can't be sure because I'm tired, but I have a vague feeling that this may be what the issue is-something in the back of my mind says that there is an alternate reconstruction which is very similar to the bulk, which will appear under the right experimental conditions.

I'll give this a try next, and put up the (hopefully) success story when the calculation completes. Happy to hear any other advice

8

General Questions and Answers / Surface geometry optimisation

« on: November 15, 2011, 06:50 »

Hi,
I'm currently trying to look at the electronic properties of surface modified (100) diamond, and have started by initially trying to get the correct geometry of the bare surface and some simple, well known systems. I'm having trouble with the optimisation process; I start with the database diamond structure, cleave it along 100, replicate along x,y and z, and then set up the optimisation and send it to the job manager. The calculations all run, but the surface doesn't reconstruct-the atoms in the topmost layers do shift slightly, but not dramatically enough for it to really be a reconstruction. Is there something I am missing? Are there particular, vital settings that should be used for a surface geometry optimisation that I may have missed?