Atoms in Molecules/Crystals: From Being to Interacting

Dr. Shant Shahbazian

Shahid Beheshti University

Tuesday 21 farvardin 97, 15:15-16:15 pm

Ibn Al-Haytham Hall, Physics Department


Matter is composed of atoms. This statement, in contrast to its deceptive simplicity, is the central dogma of the phenomenological atomic theory which is in the heart of modern chemistry and X-ray crystallography, molecular and condensed matter physics, and molecular biology. However, under a strict scrutiny, this statement is not easily reconcilable with quantum mechanics since attributing Hamiltonian to atoms in molecules/crystals is not generally feasible making them out of reach of traditional methods of quantum mechanics. In this lecture I will try to show why the quantum mechanical “identity” of atoms is lost when they are put in contact forming molecules, clusters or crystals. Then, I will show how from a “bottom-up” viewpoint this identity may partially retrieved assuming atoms in molecules/crystals as “effective quantum subsystems”. Such effective theory reveals the enormous complexity of atomic interactions. Next, I will show that a novel “top-down” approach is also conceivable that retrieves the identity of atoms as “patterns” from many-body wavefunctions. In this viewpoint each atom carries a portion of total system properties while the interactions of atoms reveal a hidden communication “network” between atoms. Finally, I will consider all these in the more general context of reductionism and emergence in physics