Density Functional Tight Binding (DFTB) methods have been shown to be capable of producing reliable molecular structures and energetics at a significantly reduced computational cost. The development and characterization of such methods will permit calculations of properties and simulations of dynamic chemical processes for molecules with many thousands of atoms. This capability will facilitate the study of proteins, nanoparticles, and other interesting species in realistic chemical environments. Ultimately, these methods will aid in the interpretation of experimental data and in the optimization of molecules targeting specific properties.
Presently the study by quantum chemistry techniques of large (several thousands of atoms) molecular systems is limited by large computer time and space (memory, disk) requirements. The required time, memory, and disk space to solve the requisite equations typically increase exponentially with the number of atoms in the systems whereas the speed and storage capacity of computers is increasing only linearly. In order to meet the requirements of the current and next generation of research topics, reliable methods which scale much more favorably with the problem size must be implemented. Tight binding (TB) methods based on density functional theory (DFT) have been shown to produce results of good accuracy at a significantly reduced computational expense. The use of such methods allows computational investigation of large molecular systems on resources which are readily available to most researchers.
Many chemical problems of current interest involve large numbers of atoms (relative to the current capability). Examples of such problems include the simulation of proteins in aqueous solution, prediction of the structure and properties of core-shell nanostructures, prediction of the current-voltage behavior of nano-molecular electronics, and simulation of aerosols. The extension of the DFTB method described to parallel computing architectures will allow the study of each of these systems via quantum chemical techniques, something which is difficult or impossible with traditional quantum chemistry methods.