Kh1015DFT
Density Functional Theory
In a top-down modelling strategy, the behaviour of materials are predicted by extracting empirical parameters [1]. Conversely, in a bottom-up strategy, the properties of materials are predicted using quantum mechanics, which is a fundamental theory of materials [1].
Density Functional Theory (DFT) is a very effective technique for studying molecules, nanostructures, solids and surfaces and interfaces. DFT is categorized under a bottom-up ab-initio approach.
Many material properties involve it being in a bulk of hundreds of thousands of atoms. Direct DFT is not feasible to model materials in bulk. QM/MM model is used instead where the bulk is sub-divided into quantum mechanics (QM) and molecular mechanics (MM) sub-systems, where a classical Newtonian description is sufficient [1].
For example, in the modelling of crack propagation in brittle solids, the bulk could be described using linear elasticity theory. Only the crack tip and an area surrounding it need to be modelled using ab-initio QM method [1].
Other than understanding the properties of existing materials, DFT has also been used to predict the properties of materials yet to be made. For example, the discovery of BiPt as a superior catalyst for hydrogen production than pure Pt was done computationally. Subsequently, Greeley et al. successfully synthesized the new material [2].
There are several known instances where DFT breaks down: inaccuracy when describing van der Waals binding of biological molecules, red-shift in the optical absorption spectra and inaccurate prediction of some non-metallic transition metal oxides to be metallic [1].