On Achieving High Accuracy in Quantum Chemical Calculations of 3d Transition Metal-Containing Systems: A Comparison of Auxiliary-Field Quantum Monte Carlo with Coupled Cluster, Density Functional Theory, and Experiment for Diatomic Molecules

Abstract

The bond dissociation energies of a set of 44 3d transition metal-containing diatomics are computed with phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) utilizing a correlated sampling technique. We investigate molecules with H, N, O, F, Cl, and S ligands, including those in the 3dMLBE20 database first compiled by Truhlar and co-workers with calculated and experimental values that have since been revised by various groups. In order to make a direct comparison of the accuracy of our ph-AFQMC calculations with previously published results from 10 DFT functionals, CCSD(T), and icMR-CCSD(T), we establish an objective selection protocol which utilizes the most recent experimental results except for a few cases with well-specified discrepancies. With 1 arXiv:1901.09464v1 [physics.chem-ph] 27 Jan 2019 the remaining set of 41 molecules, we find that ph-AFQMC gives robust agreement with experiment superior to that of all other methods, with a mean absolute error (MAE) of 1.4(4) kcal/mol and maximum error of 3(3) kcal/mol (parenthesis account for reported experimental uncertainties and the statistical errors of our ph-AFQMC calculations).In comparison, CCSD(T) and B97, the best performing DFT functional considered here, have MAEs of 2.8 and 3.7 kcal/mol, respectively, and maximum errors in excess of 17 kcal/mol for both methods. While a larger and more diverse data set would be required to demonstrate that ph-AFQMC is truly a benchmark method for transition metal systems, our results indicate that the method has tremendous potential, exhibiting unprecedented consistency and accuracy compared to other approximate quantum chemical approaches.

Predicting Ligand-Dissociation Energies of 3d Coordination Complexes with Auxiliary-Field Quantum Monte Carlo

“…This approach performs most efficiently when the ligand being removed is small, as indicated by our previous work in which the reduction in statistical error vs the uncorrelated approach was several times larger for MnH than for MnCl. 40 Similar behavior is found for the transition metal complex systems studied here, as shown in Fig. 2 for [Cu(H 2 ) 4 ] + .…”

“…[31][32][33][34][35] However, the reliability of CC methods for transition metal systems, even when multireference effects are approximated, has been the subject of vigorous debate, as illustrated by recent studies on transition metal diatomic-ligand systems. 24,[36][37][38][39][40][41] de Oliveira-Filho and co-workers found that even multireference CCSD(T) could not predict the bond dissociation energies (BDEs) for some diatomics accurately with respect to experimental measurements. A recent study by Head-Gordon and co-workers found that high levels of CC, up to CCSDTQ, are required for chemical accuracy against an exact method known as Adaptive Sampling Configuration Interaction (ASCI) results, albeit in a small basis set.…”

Singlet–Triplet Energy Gaps of Organic Biradicals and Polyacenes with Auxiliary-Field Quantum Monte Carlo

“…For ionization and bonddissociation energies of transition metal atoms and diatomics, respectively, this yielded very high accuracy while reducing the computational cost compared to double-precision calculations. 61,62 For pentacene, the largest molecule considered in this work, we verified with separate calculations in the STO-3G basis that single-and double-precision calculations gave statistically indistinguishable results.…”

An auxiliary-Field quantum Monte Carlo perspective on the ground state of the dense uniform electron gas: An investigation with Hartree-Fock trial wavefunctions

“…AFQMC has been successfully applied in recent years to a number of challenging problems in both quantum chemistry [29][30][31][32][33] and solid state physics [34][35][36] . However, the broad applicability of the method is not as well under-stood as more traditional quantum chemistry approaches which have seen decades worth of sustained development and benchmarking.…”

“…Often short determinantal expansions from complete active space self-consistent field (CASSCF) wavefunctions 31,33 or non-orthogonal multi-Slater deteraminant trial wavefunction 32 can help to restore the accuracy of the method. However, since multideterminant wavefunctions scale exponentially with system size, this approach to improving the trial wavefunction is ultimately limited, particularly for large scale applications.…”