Ryan P. Steele

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Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package,(More)
A summary of the technical advances that are incorporated in the fourth major release of the Q-CHEM quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation(More)
Many chemical reactions in atmospheric aerosols and bulk aqueous environments are influenced by the surrounding solvation shell, but the precise molecular interactions underlying such effects have rarely been elucidated. We exploited recent advances in isomer-specific cluster vibrational spectroscopy to explore the fundamental relation between the hydrogen(More)
Accurate potential energy surfaces for benzene.M complexes (M = Li+, Na+, K+, and NH4+) are obtained using coupled-cluster theory through perturbative triple excitations, CCSD(T). Our computations show that off-axis cation-pi interactions, where the cation is not directly above the aromatic ring, can be favorable and may influence molecular recognition.(More)
For a system which undergoes electron or energy transfer in a polar solvent, we define the diabatic states to be the initial and final states of the system, before and after the nonequilibrium transfer process. We consider two models for the system-solvent interactions: A solvent which is linearly polarized in space and a solvent which responds linearly to(More)
A time-reversible, multiple-timestep protocol is presented for ab initio molecular dynamics simulations using correlated, wavefunction-based underlying potentials. The method is motivated by the observation that electron correlation contributions to forces vary on a slower timescale than their Hartree-Fock counterparts. An efficient dynamics algorithm,(More)
We present a new algorithm for analytical gradient evaluation in resolution-of-the-identity second-order Møller-Plesset perturbation theory (RI-MP2) and thoroughly assess its computational performance and chemical accuracy. This algorithm addresses the potential I/O bottlenecks associated with disk-based storage and access of the RI-MP2 t-amplitudes by(More)
On-the-fly, ab initio classical molecular dynamics are demonstrated with an underlying dual basis set potential energy surface. Dual-basis self-consistent field (Hartree-Fock and density functional theory) and resolution-of-the-identity second-order Møller-Plesset perturbation theory (RI-MP2) dynamics are tested for small systems, including the water dimer.(More)
Basis set pairings for dual-basis calculations are presented for the aug-cc-pVXZ (X = D, T, Q) series of basis sets. Fidelity with single-basis results is assessed at the second-order Møller-Plesset perturbation theory (MP2) level within the resolution-of-the-identity (RI) approximation, using the S22 set of noncovalent interactions and a series of electron(More)
Local-mode coordinates have previously been shown to be an effective starting point for anharmonic vibrational spectroscopy calculations. This general approach borrows techniques from localized-orbital machinery in electronic structure theory and generates a new set of spatially localized vibrational modes. These modes exhibit a well-behaved spatial decay(More)