Dirac's dream: Understanding metal sorption by geomedia using density functional theory

Density functional theory (DFT) can provide accurate, computationally-manageable, first-principles characterizations of mineral surface speciation at molecular scales. This is accomplished by solving the Kohn-Sham equation, a tractable method of applying quantum mechanics to multi-electron systems that was inspired by some visionary remarks of P. A. M. Dirac, one of the founders of quantum theory. Fifty years of advances in DFT and the development of massively-parallel computing platforms have paved the way for molecular-scale modeling of the mineral surface that is directly relevant to the study of natural nanoparticles. In fact, DFT has matured sufficiently to be applied to metal sorption by geomedia as a “computer experiment,” yielding quantitative molecular-scale information that fully complements insights gained from surface spectroscopy. This powerful approach is illustrated first through a series of structural simulations of chalcophanite group minerals and hetaerolite-hausmannite solid solutions, then through several recent studies by the authors and their collaborators focusing on transition and heavy metal sorption by layer-type Mn(IV) oxide and Fe(II) sulfide nanoparticles. Our results show how DFT simulations reveal the mechanistic basis of metal partitioning trends observed experimentally while creating useful models for resolving experimental surface speciation conundrums.