DFT for configuration of atoms

[mrandersdk]

Hey.

I got a locked configuration of atoms, that is there positions are fixed. I would like to calculate the energy of this configuration and also the electron density. I've looked around on the internet and in some books and found that maybe Density Functional Theory (DFT) is the answer. If for example each atom has 2 electrons, and there are 5 atoms, can I just solve the kohn sham equation (where the external potetial is the one generated from the 5 atoms) in a self consistent way and get all these things

http://en.wikipedia.org/wiki/Kohn–Sham_equations.

I meen will this give me a electron density where some of the atoms are bonding and some are not, that is will the electron density be directional between bonding atoms. If this is a way to solve my problem can anyone give me some litterature that describes how to make these calculations numerically.

 

[alxm]

Well there are two ways to get your energy; either by solving the Schrödinger equation (wavefunction methods) or using DFT. Either way will give you the electron density, since in the former case it's just the sum over the squares of the orbitals and occupancies.

The difficulty of solving the Kohn-Sham equations depends on what functional you're using, i.e. how you approximate E_{xc}. (which is not known exactly)

I meen will this give me a electron density where some of the atoms are bonding and some are not, that is will the electron density be directional between bonding atoms. If this is a way to solve my problem can anyone give me some litterature that describes how to make these calculations numerically.

Well, yes. But what's the problem you're trying to solve? To figure out whether two atoms are bonding? (in addition to the energy) In practice that wouldn't typically be done by looking at the density itself, but the occupancies of the orbitals.

Anyway, there's any number of books on how to do the calculations (pretty much anything with 'quantum chemistry' in the title or subject), but it's not an entirely trivial task. Besides the difficulty, it'd also be drastic overkill to implement the whole thing just to calculate a single system or two! There's plenty of wavefunction and DFT software out there, some of which is free. A particularly popular (and free) program is http://www.msg.ameslab.gov/GAMESS/" .

 

[mrandersdk]

What i need is: Given a configuration of atoms (In my case carbon atoms), that I decide, what is the energy of the configuration and which atoms bonds and is it a sp2 or sp3 bond.

For example if i place my atoms in a graphite like structure, it should give me a low energy and the bonds should be sp2, if i place them in a diamond structure the energy should be higher and the bonds should be sp3. In my case i need to place the atoms in all kinds of configurations, and then see what the energy is, and if possible to define it, what bonds they make.

Hope it makes sense.