Development and Implementation of a Frozen-Orbital Environment within the Incremental Scheme

In this work the development of a frozen-orbital environment for the use within the incremental scheme is introduced. The implementation has been realized as a part of the Quantum Objects Library (QOL), which has been developed at the Institute for Theoretical Chemistry at the University of Cologne. The generation of the frozen-orbital environment is derived from the model potential ansatz for the valence approximation of atoms and is transfered to the application of molecular systems. The combination of this valence approximation and the correlation approximation of the incremental scheme is explained and its advantages to current incremental scheme approaches is analyzed. The necessary modification of the model potential Hamiltonian for this application and the resulting accuracy is discussed for different molecular systems. The presented implementation offers the application of the incremental scheme to molecular clusters. Besides significantly reduced wall times for the calculations, the proposed scheme also requires only a fraction of the memory resources compared to previous realizations of the incremental scheme.