Atomistic simulation technique is a unique melting pot of fundamental principles of physics, our knowledge of chemical composition of matter and the modern computer technology. The salient feature of the technique is that it offers a very high degree of "magnification" of matter allowing us to examine their structural and dynamic behaviour at an atomic scale. Better termed as "computer experiment" the technique serves the bridge between experimental and theoretical approaches. In addition to its unique predictive capability computer simulation technique is of great use in better interpretation of experimental data as well as in refinement of theoretical models. Thanks to the revolutionary developments in the past two to three decades, the technique is now one of the most favorite scientific probes in such diverse fields of science as catalysis, materials science, electro chemistry, drug discovery, geochemistry, atmospheric sciences, environmental science, etc.