Is there an optimum number of k points in the irreducible Brilloiun zone that is necessary for good calculations of bulk total energy?

[Hitanshu Sachania]

I'm using a genetic algorithm based global optimisation package, USPEX, to search stable structures of non-stoichiometric transition metal compounds. The code has a limitation - we aren't able to specify the number of k points explicitly, instead only a value called 'kresolution' can be entered. Higher is this value, lower is the density of the k grid. The thing is that it uses the same value of kresolution for all of the structures it searches. I get somewhere around 600 k points in the irreducible Brillouin zone for triclinic structures, which for most part are just slightly distorted versions of other crystal systems (cubic, hexagonal, monoclinic, etc), whereas I get anywhere around 30 to 70 k points for structures other than triclinic, all of these for the same value of kresolution. How reliable are these calculations? Can you please shed some light on what we may call an optimum number of k points in the irreducible Brillouin zone.

[K K Sram]

hi

i am writing this with some basic usage of VASP. not sure if it really helps you.

I am using VASP. thought i do not exactly able to answer your your question, in general for a crystal structure subjected to relaxation of geometry to get lower energy, we use a K-point grid as 33/a, 33/b, 33/c where a,b,c are lattice parameters.  so for example my crystal's lattice parameters are 3.2, 3.2, 5.02 then k-mesh will be [10 10 6]. the actual k-points will be internally generated.

by the way this group is still need to grow with more people who uses these softwares, so that we can share our knowledge. please encourage all your known contacts who does such research to join this.

[Hitanshu Sachania]

Hello K K Sram, that is a very new piece of information for me. Never heard of this 33/a... rule. Are you saying that the number of k points is solely dependent on the size of the supercell and not on the type of system - i.e. metals, semiconductors, insulators, cubic crystals, hexagonal crystals, triclinic crystals, intermetallics, etc.? 

And yes these google groups are really helpful. I'll definitely spread the word around.

[K K Sram]

hi Hitanshu

i generally use this principle for semiconductor crystals in Bulk and two-dimensional levels. as mentioned earlier, my knowledge on this is very limited, so i cannot really answer your query. But i know metallic systems require more k-points than semiconductor systems. if any more experienced member is there, they could enlighten all.

On Sun, Jul 15, 2018 at 12:30 AM, Hitanshu Sachania <hitanshus...@gmail.com> wrote:

Hello K K Sram, that is a very new piece of information for me. Never heard of this 33/a... rule. Are you saying that the number of k points is solely dependent on the size of the supercell and not on the type of system - i.e. metals, semiconductors, insulators, cubic crystals, hexagonal crystals, triclinic crystals, intermetallics, etc.? 

And yes these google groups are really helpful. I'll definitely spread the word around.

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