First principles investigation of strongly correlated electronic systems by the MCSCF cluster method

Adriana Moreo

'Numerical Studies of Strongly Correlated Electronic Systems' published in 'Electronic Properties of Solids Using Cluster Methods'

Brigitte Hänger

Athanasios Papastathopoulos-Katsaros

We introduce three novel cluster-based methods to describe the ground states of strongly-correlated systems such as iron-sulfur clusters, conjugated hydrocarbons, and superconductors. These methods utilize a spatial tiling of sites as their core principle. The first approach employs unrestricted cluster mean-field theory (UcMF), with clusters of Sz eigenstates. Correlations between tiles are accounted for using perturbation theory (cPT2) and coupled-cluster (cCCSD). The second approach, generalized cluster mean-field theory (GcMF), allows Sz to break in each cluster, partially including missing intercluster correlations. A projection scheme, Sz GcMF, restores global Sz symmetry for further improvement. The third approach, a non-orthogonal configuration interaction-based theory (LC-cMF) which is still in development, is based on linear combinations of different system tilings. Various criteria, such as translational symmetry and spatial proximity, guide the selection of these tilings. Benchmark calculations on one- and two-dimensional spin models show the promise of these methods. GcMF and Sz GcMF provide a qualitative improvement over UcMF, while cPT2, cCCSD, and LC-cMF can quantitatively capture inter-cluster interactions in some systems. Overall, cluster-based methods offer valuable tools for investigating strongly-correlated spin systems with potential for further advancement.

Hong Yao

한명준

Yongxin Yao, J. Liu, C. Liu +3 more

We present an efficient \textit{ab initio} method for calculating the electronic structure and total energy of strongly correlated electron systems. The method extends the traditional Gutzwiller approximation for one-particle operators to the evaluation of the expectation values of two particle operators in a full many-electron Hamiltonian. The method is free of adjustable Coulomb parameters, and has no double counting issues in the calculation of total energy, and has the correct atomic limit. We demonstrate that the method describes well the bonding and dissociation behaviors of the hydrogen and nitrogen clusters. We also show that the method can satisfactorily tackle great challenging problems faced by the density functional theory recently discussed in the literature. The computational workload of our method is similar to the Hartree-Fock approach while the results are comparable to high-level quantum chemistry calculations.