ngkpt for geometry optimization

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mdsimulationgroup
Posts: 13
Joined: Mon Feb 25, 2019 2:20 pm

ngkpt for geometry optimization

Post by mdsimulationgroup » Mon Feb 25, 2019 2:32 pm

Hello,

I'm very new to planewave calculations; all of my experience is gaussian basis sets. I'm trying to get a feel for the kpoint grid. If all I want to do is geometry optimization of a slab of copper with a molecule absorbed to the surface, how should I be setting my ngkpt? Is it out to have a sparse grid such as:

ngkpt 1 1 1

Or should I have more points?

Thanks,
Stacey

ebousquet
Posts: 313
Joined: Tue Apr 19, 2011 11:13 am
Location: University of Liege, Belgium

Re: ngkpt for geometry optimization

Post by ebousquet » Tue Feb 26, 2019 3:52 pm

Dear Stacey,
When doing a slab, you have one direction that is very large with vacuum (probably the z direction), meaning that your reciprocal space is very small and then the number of k-point can be set to 1 in this direction to have good precision. In the other directions, you need to test the convergence of the k-point grid, i.e. check how your result change w.r.t. number of k-point along x and y (it will depend if you are metallic or not and what is the size of the cell in these directions).
Best wishes,
Eric

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