The quantum size effect and very strong electron correlation are two hallmarks of nano electronic structure.  While the quantum size effect is a one electron property, electron correlation involves interactions among the electrons.  In electronic structure theory, electron-electron repulsion causing correlation is normally considered only in an average (or mean field) sense, as for example in a single Hartree-Fock determinant.  This is the simple molecular orbital model which is often a good approximation for molecules.  In infinite systems this averaging treatment leads to delocalized electronic bands -- an excellent description of bulk 3D sp<sup>3</sup> semiconductors. However in reality electrons try to instantaneously avoid each other; their relative motion is correlated.  In nanoscience strong electron-electron repulsion and correlation create new collective states and cause new femtosecond kinetic processes.   This is especially true in 1D and 2D systems.   I discuss strong correlation in carbon nanotubes, graphene, zero dimensional quantum dots, , trans-polyacetylene chains, transition metal dichalcogenides, organic/inorganic Pb iodide perovskites, and pentacene van der Waals crystals.   The independent contributions of screening and dimensionality are analyzed.  <br/>

Size, dimensionality and strong electron correlation in nanoscience

254th National Meeting (2017)

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