For large systems, <i>ab initio</i> calculations can be prohibitively expensive and one typically has to give up some accuracy as the system size increases. This, for example, makes density functional theory (DFT), with its practical limitations, the method of choice for big systems. We explore a new approach which aims to obtain high accuracy for huge systems without too much computational effort. This method develops empirical Hamiltonians from <i>ab initio</i> multireference configuration interaction (MRCI) data of atoms and diatomic molecules. These Hamiltonians are then used in the prediction of both ground and excited state properties of larger systems. Applications to different silicon clusters and bulk silicon are presented.

Semi-empirical Hamiltonians from ab initio MRCI data on atoms and diatomics

ACS Spring 2022

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