Böcker av Mukherjee Bijit

Born-Oppenheimer (BO) theory and its treatment for solving molecular Schr¿odinger Equation(SE), as proposed1 in 1927 and later on with Huang2 in 1954, has been the cornerstoneof our understanding of chemical processes employing quantum chemistry. The triumphof BO treatment lies on the huge mass difference of electrons and nuclei allowing us toseparate their motions while studying molecular quantum mechanics. The approximationallows us to study the electron dynamics which parametrically depends on the nuclearpositions. In the limiting situation of such mass differences (me MN), the BOapproximation could able to describe some of the chemical processes satisfactorily thatmainly occur at lower energy regimes of ground electronic state. However, nature exhibitsa whole range of molecular phenomena where we observe a violation of such a'celebrated' approximation. These situations arise whenever electronic and nuclear motiongets coupled owing to different reasons that leads to what is known as nonadiabaticevents. Simplest instances are photosynthesis, vision, charge transfer chemical reactions,solar energy conversion and photochemical reactions, all of which involve electronicallyexcited states and thus, cannot be fully accounted for if considered solely from a BO per-spective. Owing to such range of nonadiabatic phenomena, failure of BO approximationis encountered quite often in nature rather than rarely.