Cyclic cluster approach to three-dimensional solids: Quasi-relativistic INDO treatment

A recent implementation of the cluster crystal orbital (CCO) method for ele ctron structure calculations of solids within the quasi-relativistic INDO t reatment has been tested for a wide scale of model systems including insula tors, semiconductors, metals, semimetals, and superconductors. Within the m ethod, a sufficiently large portion of the crystal is essentially treated a s a supermolecule (cluster) in which, due to imposed cyclic Born-Karman bou ndary conditions, all the unit cells experience-the same surroundings, whil e all the interactions within the cluster are preserved. Hence, unwanted ef fects due to the cluster boundaries are removed, and transition into the co mplex quasi-momentum space is made possible and uniquely defined. Within th e approach, the advantages of the crystal orbital method and the simple clu ster model are linked simultaneously, The current implementation, based on the quasi-relativistic INDO Hamiltonian and parametrized for all elements o f the periodic table, allows for very fast SCF calculation of clusters cont aining tens of thousands of atoms. A reasonable balance is reached between the physical model considered (sufficient scope of long-range interactions, large enough number of k-points) and the rigorousness of the method used ( type of the Hamiltonian and wave functions used).