On fermionic shadow wave functions for strongly correlated multi-reference systems based on a single Slater determinant

Abstract

-We demonstrate that extending the Shadow Wave Function to fermionic systems facilitates to accurately calculate strongly-correlated multi-reference systems such as the stretched H2 molecule. This development considerably extends the scope of electronic structure calculations and enables to efficiently recover the static correlation energy using just a single Slater determinant.Introduction. -One of the most outstanding problems of computational physics and quantum chemistry is the ability to devise a quantitatively precise, yet computationally tractable, method to accurately break a chemical bond across an entire reaction coordinate. A particularly simple example is the H 2 molecule, in particular when the covalent bond between the H atoms is stretched. Effective single-particle theories, such as the widely employed Hartree-Fock (HF) or Density Functional Theory (DFT) methods, describe the covalent bond well, but the energy is severely overestimated upon dissociation [1]. This wellknown problem is attributed to the multi-reference character of the stretched H 2 molecule, or static electron correlation that arises in situations with degeneracy or neardegeneracy, as in transition metal chemistry and stronglycorrelated systems in general [2]. As a consequence, the stretched H 2 molecule and similar problems are typically dealt with using multi-determinant wave functions [3]. However, for larger systems with many degeneracies, the number of determinants quickly becomes unfeasible [4,5].

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