OTI Lumionics (Canada)

Metal-Nitrogen-Carbon motifs present intriguing structural and electronic properties for a number of applications, including as oxygen reduction catalysts. However, computational investigations of M-N-C-catalyzed reactions have must grapple with their complex electronic structures. In the present study, we evaluate the impact of the density functional approximation on calculated M-N-C catalyst activities for oxygen reduction. Using metalloporphyrins as model catalysts, we find a significant split between pure (GGA) and hybrid functionals, with hybrid functionals, in particular B3LYP, showing greater agreement with DLPNO-CCSD(T) reaction energies. Notably, double-hybrids offered no noticeable improvement over the much more computationally efficient B3LYP and PBE0. Other discrepancies between functionals, including ground state spin and geometry, are also considered in this work. Finally, both hybrid and double-hybrid functionals greatly reduced the gas phase errors associated with the main group molecules in the oxygen reduction reaction relative to GGA calculations, leading us to question the application of widely used empirical corrections to O$_2$.

We present an efficient method for construction of a fully anticommutative set of Pauli generators (elements of the Pauli group) from a commutative set of operators that are composed exclusively from Pauli x̂ operators (purely X generators) and sorted by an associated numerical measure, such as absolute energy gradients. Our approach uses the Gauss-Jordan elimination applied to a binary matrix that encodes the set of X generators to bring it to the reduced row-echelon form, followed by the construction of an anticommutative system in a standard basis by means of a modified Jordan-Wigner transformation and returning to the original basis. The algorithm complexity is linear in the size of the X set and quadratic in the number of qubits. The resulting anticommutative sets are used to construct the qubit coupled cluster Ansatz with involutory linear combinations of anticommuting Paulis (QCC-ILCAP) proposed in J. Chem. Theory Comput. 2021, 17 (1), 66-78. We applied the iterative qubit coupled cluster method with the QCC-ILCAP Ansatz to calculations of ground-state potential energy curves for symmetric stretching of the water molecule (36 qubits) and dissociation of N2 (56 qubits).