H: A model system for assessing the performance of diffusion Monte Carlo calculations using a single Slater determinant trial function.

A model H system is used to investigate the accuracy of diffusion Monte Carlo (DMC) calculations employing a single Slater determinant to fix the nodal surface. The lowest energy singlet state of square H is a diradical which is poorly described by DMC calculations using a single determinant (SD) trial function. Here we consider distortions to rectangular structures, which decrease the amount of diradical character.

Quantum Monte Carlo calculation of the binding energy of the beryllium dimer.

The accurate calculation of the binding energy of the beryllium dimer is a challenging theoretical problem. In this study, the binding energy of Be2 is calculated using the diffusion Monte Carlo (DMC) method, using single Slater determinant and multiconfigurational trial functions. DMC calculations using single-determinant trial wave functions of orbitals obtained from density functional theory calculations overestimate the binding energy, while DMC calculations using Hartree-Fock or CAS(4,8), complete active space trial functions significantly underestimate the binding energy.

Theoretical study of the binding energy of a methane molecule in a (H2O)20 dodecahedral cage.

The interaction energy of a methane molecule encapsulated in a dodecahedral water cage is calculated using the MP2, MP2C, various dispersion-corrected DFT, and diffusion Monte Carlo (DMC) methods. The MP2, MP2C, and DMC methods give binding energies of -5.04, -4.

Benchmark study of the interaction energy for an (H2O)16 cluster: quantum Monte Carlo and complete basis set limit MP2 results.

The quantum Monte Carlo method is used to calculate the binding energy of an (H2O)16 cluster that has been the subject of several recent theoretical studies. The resulting interaction energy, -165.1(8) kcal/mol, is very close to our MP2 complete basis set limit interaction energy of -164.

Correlation Consistent Gaussian Basis Sets for H, B-Ne with Dirac-Fock AREP Pseudopotentials: Applications in Quantum Monte Carlo Calculations.

In this paper, we introduce correlation consistent Gaussian-type orbital basis sets for the H and B-Ne atoms for use with the CASINO Dirac-Fock AREP pseudopotentials. These basis sets are tested in coupled cluster calculations on H2, B2, C2, N2, O2, and F2 as well as in quantum Monte Carlo calculations on the water monomer and dimer and the water-benzene complex, where they are found to give low variances in variational Monte Carlo calculations and to lead to reduced time step errors and improved convergence in diffusion Monte Carlo calculations compared to the use of nonoptimized basis sets. The use of basis sets with a large number of contracted s and p primitives is found to be especially important for the convergence of the energy in the diffusion Monte Carlo calculations.

Generalized theory for nanoscale voltammetric measurements of heterogeneous electron-transfer kinetics at macroscopic substrates by scanning electrochemical microscopy.

Here we report on a generalized theory for scanning electrochemical microscopy to enable the voltammetric investigation of a heterogeneous electron-transfer (ET) reaction with arbitrary reversibility and mechanism at the macroscopic substrate. In this theory, we consider comprehensive nanoscale experimental conditions where a tip is positioned at a nanometer distance from a substrate to detect the reactant or product of a substrate reaction at any potential in the feedback or substrate generation/tip collection mode, respectively. Finite element simulation with the Marcus-Hush-Chidsey formalism predicts that a substrate reaction under the nanoscale mass transport conditions can deviate from classical Butler-Volmer behavior to enable the precise determination of the standard ET rate constant and reorganization energy for a redox couple from the resulting tip current-substrate potential voltammogram as obtained at quasi-steady state.