Colloquium: “Uncovering the Inner Lives of Electrons” – Wednesday, April 17, 2019, at 4:00 PM

What happens when two substances are mixed together? Does a chemical reaction occur? If so, which chemical bonds are broken? What new chemical bonds are formed? Can we increase the efficiency of the reaction by changing the conditions under which it occurs? Questions like these lie at the core of chemistry. Addressing them requires understanding, at a fundamental level, how the electrons that bind atoms into molecules rearrange during the course of a chemical reaction and, more subtly, how different molecular environments influence these rearrangements. Therefore, in order to understand the nature of the chemical bond, and to master the chemical reactions by which chemical bonds are fractured and formed, we must uncover the inner lives of electrons.
The physical laws regulating how electrons behave in a molecular environment are encapsulated by the electronic Schrödinger equation. Unfortunately, highly-accurate solutions to the Schrödinger equation are rarely available for molecules containing more than four electrons, while most molecules of interest to chemists contain hundreds, or even thousands, of electrons. This impels the development of approximate models for electronic behavior. Such models are only effective in certain special cases. For example, it is relatively easy to describe cases where the electrons in a molecule move nearly independently, so that the motion of one electron does not affect the other electrons very much. It is also relatively easy to describe cases where the electrons in a molecule are rigidly correlated, so that moving one electron causes the other electrons to move in a nearly deterministic way. The electrons in most chemical substances lie between these two extremes, and developing practical computational methods for these in-between cases is the primary challenge of modern quantum chemistry. In this talk, I will reveal how quantum chemists develop new models for the behavior of electrons in molecules and materials. Some of the new methods are practical even for large molecules containing hundreds of electrons.

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