Section: New Results

Algorithms for Orbital-Free Density Functional Theory

Participants : Francois Rousse, Stephane Redon.

The Schrödinger equation permits, in theory, to model and simulate every molecular systems exactly. Unfortunately it is not computationally doable to solve this equation even on really small systems (2 atoms). Density Functional Theory (DFT) gives a method to solve this equation, find the electronic structure and simulate molecules with the laws of physics on reasonably large system : from 1.000 to 10.000 depending on the basis chosen and the version of DFT used. Unfortunately, the computation of kinetic energy requires the orthogonalization of the basis, which consumes a lot of time and prevents the algorithm from being adaptive : one needs to recompute the whole system if a little change is done in the molecules position. One can deals with this issue by computing the kinetic energy directly with the electronic density and not anymore with the orbitals. That is the idea of Orbital-Free DFT (OF-DFT). It can models great systems (up to 1.000.000 atoms) and be turned adaptive. On the other hand, it looses a lot of accuracy and power to model different kind of systems on the other DFT.

We have already developed our own OF-DFT code. It runs on parallel cores, is implemented in the SAMSON platform as a SAMSON App and gives correct electron's densities. The electronic structures are computed in real space to preserve the possibility of incremental calculations. We are now going to test our implementation, and will then attempt to make the method adaptive. The difficulty will be the determination of the domain that needs to be recomputed when a part of the system has moved, and the criteria that will help to do so.