Evolution Of Density Functional Theory (DFT)

Evolution of Density Functional Theory (DFT)

Quantum Theory

The idea of atom existed as early as the Greek and Indian civilizations, but more as a philosophical thought rather than a well-defined theory based on empirical evidence. Atom was assumed as something that is indestructible and the smallest component that makes up matter. It took almost 2000 years for the development of modern day atomic theory with proof for the existence of atoms and further subatomic particles. The archaeological classification of human history as stone age, bronze age and iron age depicts the evolution of macroscopic chemistry first. Much later through the fundamental studies in electromagnetism and blackbody radiation, the discovery and theoretical formulation

Hohenberg and Kohn (1964), Kohn and Sham (1965) published two seminal papers laying a strong foundation for Modern Density Functional Theory (DFT). They found that the wave function is over specified (similar to Dirac 's observation) and a two electron probability density is good enough to get the molecular energy. DFT formalism has a lot of inherent assumptions, such as Local Density Approximation and the choice of functional has to be tackled carefully [5]. The main advantage of DFT is its ability to handle large systems and the low computational cost associated. Also DFT can be employed to get the interaction potentials in Molecular Dynamics runs thus incorporating a more accurate description of underlying electronic potentials. DFT helps in the calculation of a wide range of molecular properties of real physical significance. DFT spurred the growth of solid state physics. Peter Puschnig [6] gave an extensive list of DFT applications which are reproduced here: Structural properties (lattice parameters, elastic constants, equilibrium geometry, etc.), electronic structure (band structure, density of states), lattice dynamics (vibrational frequencies, phonon density of states, vibrational entropy), electron density (charge rearrangements, electric field gradients), spectroscopy (photoemission, optical absorption, Raman scattering, Compton scattering,