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## Publications

Publications (75)

The exact expressions for the dipole, quadrupole, and octupoles of a collection of N point charges involve summations of corresponding tensors over the N sites weighted by their charge magnitudes. When the point charges are atoms (in a molecule) the N‐site formula is an approximation, and one must integrate over the electron density to recover the...

We present molecular dynamics (MD), polarizability driven MD (α-DMD) and pump-probe simulations of Raman spectra of the protonated nitrogen dimer N 4 H ⁺ , and some of its isotopologues, using the CCSD(T)-F12b/aug-cc-pVTZ based potential energy surface in permutationally invariant polynomials (PIP) due to Yu and co-workers [J. Phys. Chem. A 119, 11...

A linearly parameterized functional form for a Cartesian representation of molecular dipole polarizability tensor surfaces (PTS) is described. The proposed expression for the PTS is a linearization of the recently reported power series ansatz of the original Applequist model, which by construction is non‐linear in parameter space. This new approach...

We describe a novel variant of the driven molecular dynamics (DMD) method derived for probing Raman active vibrations. The method is an extension of the conventional μ-DMD formulation for simulating IR activity by means of coupling an oscillating electric field to the molecule’s dipole moment, μ, and inducing absorption of energy via tuning the fie...

Using calculations, we show that a proposed Cu(I)-mediated deconstructive fluorination of N-benzoylated cyclic amines with Selectfluor® is feasible and may proceed through: (a) substrate coordination to a Cu(I) salt, (b) iminium ion formation followed by conversion to a hemiaminal, and (c) fluorination involving C–C cleavage of the hemiaminal. The...

Bis(2-chloroethyl) sulfide or sulfur mustard (HD) is one of the highest-tonnage chemical warfare agents and one that is highly persistent in the environment. For decontamination, selective oxidation of HD to the substantially less toxic sulfoxide is crucial. We report here a solvent-free, solid, robust catalyst comprising hydrophobic salts of tribr...

Ligand field theory (LFT) calculations of energy levels were performed for the neutral actinide monooxides (AnO) and their singly and doubly ionized cations (AnO⁺ and AnO²⁺) by treating the molecular electronic states as Anm+ free‐ion energy levels (where An ∈ Th through Lr and m = 1, 2, 3, or 4) perturbed by the electric field of O²⁻or O⁻. LFT par...

Radical enhanced intersystem crossing (EISC) of organic chromophores is an important approach to generate a long-lived triplet state for various electronic and optoelectronic applications. However, structural factors and design rules to promote EISC are not entirely clear. In this work, we report a series of boron dipyrromethene (BODIPY) derivative...

The counterions of polyoxometalates (POMs) impact properties and applications of this growing class of inorganic clusters. Here, we used density functional theory (DFT) to elucidate the impact of fully hydrated alkali metal cations on the geometry, electronic structure, and chemical properties of the polyoxotungstate anion [PW12O40]³⁻. The calculat...

Indium phosphide quantum dots (InP QDs) are nontoxic nanomaterials with potential applications in photocatalytic and optoelectronic fields. Post-synthetic treatments of InP QDs are known to be essential for improving their photoluminescence quantum efficiencies (PLQEs) and device performances, but the mechanisms remain poorly understood. Herein, by...

The threat of chemical warfare agents (CWAs), assured by their ease of synthesis and effectiveness as a terrorizing weapon, will persist long after the once-tremendous stockpiles in the U.S. and elsewhere are finally destroyed. As such, soldier and civilian protection, battlefield decontamination, and environmental remediation from CWAs remain top...

CsPbI3 perovskite quantum dots (QDs) have shown great potential in light-harvesting and light-emitting applications, which often involve the transfer of charge carriers in and out of these materials. Here, we studied size-dependent charge separation (CS) and charge recombination (CR) between CsPbI3 QDs and rhodamine B (RhB) molecules, using transie...

The effect of hydration of anatase (0 0 1), and rutile (0 0 1), (1 0 1) and (1 1 0) surfaces of TiO2 on the rate of electron capture from an adsorbed graphene sheet is elucidated by means of computation at a level of tight-binding density functional theory. Initially, the clean surfaces are allowed to interact with bulk water. Following an equilibr...

We report computational studies of (O,O-dimethyl)-(O-4-nitrophenyl)-phosphate (DMNP) and (O,O-dimethyl)-(O-phenyl)-phosphate (DMPP) decomposition by the Zr-substituted Polyoxometalate {α-PW11O39Zr(μ-OH)(H2O)}⁴⁻, which has been recently shown to be a catalytic active species in the reaction of (Et2NH2)8[{α-PW11O39Zr(μ-OH)(H2O)}2]·7H2O with nerve age...

Configuration interaction ligand field theory (CI LFT) calculations of the electronic energy levels of ThO were performed by treating the molecular electronic states as Th 2+ free‐ion levels perturbed by the ligand field of O2−. Twenty nine experimentally characterized ThO v = 0 energy levels, together with the energy difference between the v = 0 l...

We describe a bulk adjusted linear combination of atomic orbitals (BA-LCAO) approach for nanoparticles. In this method, we apply a many-body scaling function (in similar manner as in the environment-modified total energy based tight-binding method) to the DFT-derived diatomic AO interaction potentials (like in the conventional orbital-based density...

Use of quantum confinement as a tool to control biexciton recombination in quantum dots is investigated theoretically for a series of quasi-Type-II and Type-I CdSe/CdS core/shell spherical quantum dots. Recent experimental measurements show that in such nanostructures, the CdS shell may act as a type of an efficient retarder for biexciton recombina...

The impact of the ambient gas molecules (X), NO2, CO2 and SO2, on the structure, stability and decontamination activity of the Cs8Nb6O19 polyoxometalate was studied computationally and experimentally. It was...

Quantum confined semiconductor nanocrystals have emerged as a new class of materials for light harvesting and charge separation applications due to the ability to control their properties through rational design of their size, shape and composition. We report here a study of enhancing the quantum yield of methyl viologen (MV2+) photoreduction using...

We describe an extension of the conventional Fourier grid discrete variable representation (DVR) to the bound state problem of a particle with a position-dependent mass. An infinite order DVR, derived for a variable mass kinetic energy operator, coupled with an efficient grid contraction scheme yields essentially exact eigenvalues for a chosen grid...

In an effort to develop robust molecular sensitizers for solar fuel production, the electronic structure and photodynamics of transition-metal-substituted polyoxometalates (POMs), a novel class of compound in this context, was examined. Experimental and computational techniques including femtosecond (fs) transient absorption spectroscopy have been...

The widely used C-H functionalization strategies and some complexities in the Pd-catalyzed chemical transformations were analyzed. It was emphasized that in the course of catalysis various Pd-intermediates (including nano-scale Pd-clusters) could act as active catalysts. However, both identification of these catalytically active species and determi...

A polyoxometalate-supported trirhenium carbonyl cluster, mimicking metal oxide supported interfacial dyadic structures, has been synthesized and characterized. Multiple techniques, including computational and transient absorption spectroscopy, have been applied to characterize the charge-transfer dynamics occurring at the interfaces of this "double...

Compounds (IIIa,b) and (Va,b) are characterized by XRD, UV/VIS spectroscopy, and DFT calculations.

Keggin and Dawson-type polyoxometalates (POMs) covalently grafted to heteroleptic cyclometalated iridium(III) complexes (POM–[Ir] dyads) have been prepared by postfunctionalization of organosilyl and organotin POM derivatives. Electronic properties of these 4 photosensitized POM–[Ir] dyads were evaluated by electrochemical measurements and theoreti...

We present results on parameterization of the Reactive Force Field [van Duin, A. C. T.; Dasgupta, S.; Lorant, F.; Goddard, W. A. "ReaxFF: A reactive force field for hydrocarbons" J. Phys. Chem. A 2001, 105, 9396-9409] for investigating the properties of the [Nb6O19Hx](8-x)- Lindqvist polyoxoanion, x=0-8, in water. Force field parameters were fitted...

A new series of complexes containing two electron donating groups, {M(CO)(3)}(+) ions, M = Re or Mn, on one polytungstate electron acceptor group have been prepared and characterized. These complexes containing two electron donating groups, {M(CO)(3)}(+) ions, M = Re or Mn, on one polytungstate electron acceptor group have been prepared and charact...

The nature of several TiO2 surfaces in liquid water, as well as the adsorption of a functionalized C60, L*C60 (where L is a carboxylic acid), on TiO2 anatase and rutile low index surfaces in vacuo and in liquid water have been studied at the self-consistent charge density functional tight-binding (SCC-DFTB) level of theory. It is shown that the SCC...

We present a comparative study of energy flow from a vibrationally excited solvated dialanine molecule to the surrounding water in the IR and THz range. We employ the driven molecular dynamics (DMD) approach to investigate the energy flow from the solute molecule to water molecules. As a result, we find a more rapid and efficient energy flow from t...

Monoprotected chiral amino acids have recently been established as a class of ligand scaffolds for effecting Pd-catalyzed enantioselective C-H bond activation reactions. However, to elucidate the mechanistic details and controlling factors of these reactions, more comprehensive studies are needed. In this work we report computational investigations...

Having closed valence sub-shells, the alkaline earth atoms participate in covalent bonding via orbital hybridization and exchange interactions, with additional contributions from dispersion interactions. Starting from a closed ns2 configuration imparts different characteristics to the chemistry of this group, as compared to metals that have open-sh...

Two hybrid materials based on the tris(bipyridine) ruthenium(II), [Ru(bpy)(3)](2+) and Keggin-type polyoxometalates, [PW(11)O(39)](7) and [PW(12)O(40)](3), namely, [Ru(bpy)(3)][K(5)PW(11)O(39)] (1) and [Ru(bpy)(3)][KPW(12)O(40)] (2) were synthesized. X-ray crystallographic study of the red-colored complex, 2, shows that it crystallizes in the ortho...

A recently suggested constrained quasiclassical trajectory (c-QCT) method for avoiding the zero-point leak in the water dimer [11] is applied to the water trimer, employing an ab initio full-dimensional potential energy surface. We demonstrate the failure of the standard/unconstrained QCT method for (H2O)3 and show the utility of c-QCT dynamics. In...

We propose a semiclassical method for correcting molecular energy levels obtained from a quantum mechanical variational calculation. A variational calculation gives the energy level (i.e., eigenvalue) as the expectation value of the molecular Hamiltonian <phi/H/phi>, where /phi> is the trial wave function. The true (i.e., exact) eigenvalue E can th...

The mechanism and electron transfer dynamics of the reaction [Ru(II)(mptpy)(2)](4+) + hnu + [S(2)O(8)](2-) --> [Ru(III)(mptpy)(2)](5+) + SO(4)(2-) + SO(4)(-*) were studied using various computational (density functional and exciton interaction theories) and experimental (transient absorption, static and time-resolved fluorescence spectroscopy, and...

We report the implementation of a previously suggested method to constrain a molecular system to have mode-specific vibrational energy greater than or equal to the zero-point energy in quasiclassical trajectory calculations [J. M. Bowman et al., J. Chem. Phys. 91, 2859 (1989); W. H. Miller et al., J. Chem. Phys. 91, 2863 (1989)]. The implementation...

Geometry and electronic structure of five species [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](10-) (1), [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](9-) (2), [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](8-) (3), [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)](7-) (4), and [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)...

We examine the mechanism of electron transfer between [Ru(bpy)(3)](2+) and [S(2)O(8)](2-) in aqueous solutions using time-dependent density functional and transition charge density model levels of theory. The calculations support the existence of a short-lived, optically bright S1 state that decays to lower-lying triplet states T1 and T2. The T1 st...

The design of viable and well-defined molecular catalysts for water oxidation is both intellectually and practically important in conjunction with the conversion of solar to chemical energy. Increasingly, high-resolution crystal structures and physicochemical investigations of the Mn4Ca-centered water oxidation-oxygen evolving center (OEC) in photo...

In this work, we present infrared spectra of H(5)O(2)(+) and its D(5)O(2)(+), D(4)HO(2)(+), and DH(4)O(2)(+) isotopologues calculated by classical molecular dynamics simulations on an accurate potential energy surface generated from CCSD(T) calculations, as well as on the BLYP DFT potential energy surface sampled by means of the Car-Parrinello algo...

We report three modifications to recent ab initio, full-dimensional potential energy surfaces (PESs) for the water dimer [X. Huang et al., J. Chem. Phys. 128, 034312 (2008)]. The first modification is a refit of ab initio electronic energies to produce an accurate dissociation energy D(e). The second modification adds replacing the water monomer co...

Low lying electronic states of the beryllium dimer were investigated by laser induced fluorescence (LIF) and resonance enhanced multiphoton ionization (REMPI) techniques. Be(2) was formed by pulsed laser ablation of Be metal in the presence of helium carrier gas, followed by a free jet expansion into vacuum. Several previously unobserved states of...

We report quantum calculations of vibrational states of trans N-methyl acetamide (H3C-HNCO-CH3) in full dimensionality using the code MULTIMODE. In this code, the full potential is represented as a hierarchical sum of n-mode potentials in the normal coordinates. All 30 one- and 435 two-mode potentials are included in the sum, as well as a restricte...

Standard molecular and driven molecular dynamics are used to analyze prominent spectral features in the H5O2+ infrared spectrum. In the driven method, the molecular Hamiltonian is augmented with a time-dependent term, mu x epsilon(0) sin(omegat), where mu is the dipole moment of H5O2+, epsilon0 is the electric field, and omega is the frequency. The...

Conventional normal-mode analysis of molecular vibrations requires computation and storage of the Hessian matrix. For a typical biological system such storage can reach several gigabytes posing difficulties for straightforward implementation. In this work we discuss an iterative block method to carry out full diagonalization of the Hessian while on...

A formulation of a direct, iterative method for obtaining the lowest eigenvalues and eigenvectors of a Hessian matrix is presented. Similar to the iterative schemes in electronic structure configuration interaction calculations (methods due to Lanczos, Davidson, and others), the mass-weighted Hessian matrix K is not constructed explicitly; instead,...

The driven molecular-dynamics (DMD) method, recently proposed by Bowman, Zhang, and Brown [J. Chem. Phys. 119, 646 (2003)], has been implemented into the TINKER molecular modeling program package. The DMD method yields frequencies and normal modes without evaluation of the Hessian matrix. It employs an external harmonic driving term that can be use...

A recently developed signal processing method has been applied to a time evolved Gaussian wave packet roughly corresponding to the ground vibrational state of protonated methane at time zero. The time evolution of the wave packet was described by semiclassical initial value representation theory where classical trajectories are used to evaluate the...

A singular value decomposition based harmonic inversion signal processing scheme is applied to the semiclassical initial value representation (IVR) calculation of molecular vibrational states. Relative to usual IVR procedure of Fourier analysis of a signal made from the Monte Carlo evaluation of the phase space integral in which many trajectories a...

Model infrared spectra for non-rotating H2O are calculated at 0 K, based on exact quantum, standard classical and semiclassical calculations. An accurate potential energy surface is used along with a realistic dipole function. An analysis of the classical and quantum spectrum in the harmonic approximation is presented at 0 K. This clearly reveals t...

A new potential energy surface and dipole moment surface were constructed for BrHI- by a 3-D spline interpolation of ab initio data at the MRCI/aVQZ level of theory and basis set, with ECP's for the halogens. "Exact"vibrational calcns. were performed on this potential energy surface for BrH(D)I- using two very different codes. The asym. stretch and...

A method recently developed for calculating vibrational spectral densities of molecules, previously tested successfully on H2O, is applied here to several larger molecules. The method relies on use of a time averaging procedure in the conventional semiclassical (SC) initial value representation (IVR) expression for the spectral density. The converg...

An application of the initial value representation IVR of semiclassical SC theory to approximate the quantum mechanical time evolution operator, expi t/, requires an integral over the phase space of initial conditions of classical trajectories. The integrand of this integral is complex, i.e., has a phase, from which quantum coherence in fact, all q...

Rotational constants for CN(X)–H2/D2(j2=1), derived from electronic spectra, exhibit an unusually small dependence on H2/D2 isotopic substitution. In the present study, variational bound state calculations were carried out to examine the origin of this effect. A four-dimensional potential energy surface [J. Chem. Phys. 110 (1999) 10380] was used fo...

Two-dimensional intermolecular potential energy surfaces for the CH(A 2Δ)–Ar complex (CH bond fixed at equilibrium) have been calculated at the multireference singles and doubles configuration interaction/correlation-consistent valence quadruple zeta level of theory. These surfaces are of 2 2A′ and 2 2A″ electronic symmetry. Both potentials define...

The photodissociation of ketene is studied using direct surface-hopping classical trajectories where the energy and gradient are computed on the fly by means of state-averaged complete active space self-consistent field with a double-zeta polarized basis set. Three low-lying electronic states, singlets S-0 and S-1 and triplet T-1, are involved in t...

The temperature dependence of the rate constant for the electronic energy transfer process I(2P3/2)+O2(a 1Δg)→I(2P1/2)+O2(X 3Σg−) has been studied theoretically. Seven ab initio diabatic potential energy surfaces, four for the entrance channel and three for the exit channel, and the coupling elements between them, were adopted. Energy transfer dyna...

Neutral beryllium clusters Ben, n=2–8, were investigated by density functional techniques. To minimize errors, geometry optimization, frequency and energy calculations were all carried out on the same level of theory, employing a large 6-311++G(3df) basis set. The method reproduces well the experimentally known bond length and vibrational frequency...

The coupled-cluster method with a large basis set with quasi-relativistic effective core potentials on the halogens was utilized to investigate the ground electronic state X 1Σ+ of the IHBr anion. A semi-global, three-dimensional potential energy surface was obtained via spline interpolation of ab initio data. Variational rovibrational calculations...

The photodissociation of chlorine peroxide, ClOOCl, is studied with classical trajectories where the energy and gradient are computed on the fly by means of the state-averaged (sa) complete active space self-consistent field (CASSCF) with the DZP(+) basis set. We show that six electronically excited states are involved in the process of decompositi...

Photodissociation of isocyanic acid, HNCO, was studied with high-level ab initio methods. Geometry optimizations of stationary points and surface crossing seams were performed with the complete active space self-consistent-field (CASSCF) method, and the energetics were re-evaluated with single-point second-order multireference perturbation theory (...

A four-dimensional potential energy surface has been calculated for the long-range interaction between rigid CN(X) and rigid H2(X). Electronic structure calculations were performed using single-reference wave function with singles and doubles configuration interaction. Davidson and counterpoise corrections were applied. The atomic orbital basis set...

An electron photodetachment spectrum of Cl3− is reported for 193 nm (6.42 eV) excitation. The spectrum was assigned using high-level ab initio calculation for the Cl3 radical and the Cl3− ion. A broad band centered around 1.25 eV (electron kinetic energy) has been assigned to the Cl3−(X1Σg+)→Cl3(X2Πu) and Cl3(12Σg+) transitions. Vertical photodetac...

Potential energy curves and electronic transition moments for Be2 were calculated using MRSDCI and EOM coupled cluster levels of theory with a (12s6p3d2f1g)/[5s4p3d2f1g] basis set. The properties of low-lying singlet, triplet, and quintet states were predicted. MRSDCI results were found to be in agreement with experimental observations. Predictions...

Ab initio electronic structure calculations have been used to investigate the electronic energy transfer processPotential energy surfaces for all states associated with the reactants and products were obtained using CASSCF and CASPT2 methods, including the effective one-electron spin–orbit Hamiltonian. Surfaces correlating with the above reactants...

We report a rigorous ab initio study of the ground and low-lying excited-state potential-energy surfaces (PESs) of the Cl3 radical at CASSCF, CASPT2, and MRSDCI levels of theory. The ground state has two Cl⋯Cl2 van der Waals complexes, XL and ′B. The linear asymmetric minimum (XL) is 2Π, with a Cl–Cl distance r = 3.90 bohr, and a Cl–M (M: the Cl2 c...

Laser absorption spectrum of the LaF $B^{1}\Pi-X^{1}\Sigma^{+}$ (2,0), (1,0), (2,1), and (3,2) bands was recorded. Gas phase LaF was obtained by heating a mixture of a 0.2 g of La metal and 0.3 g of $laF_{3}$ powder to 1900K. In order to modulate the absorption signal, the concentration of LaF was varied by passing a 25 kHz discharge (80-100W, 0.5A...

The laser absorption spectrum of the LaF+molecular ion has been observed for the first time. Gas-phase LaF was obtained by heating a mixture of La metal and LaF3powder to 1900 K. LaF+ions were produced by passing a 25-kHz discharge through the vapor. Under these conditions the tantalum heating tube used to vaporize the sample also acted as a hollow...

Ligand field theory calculations of energy levels were performed for the neutral lanthanide monohalides by treating the molecular electronic states asLn+free-ion levels perturbed by a ligand fieldX−(whereLn∈ Ce through Yb andX∈ F, Cl, Br, or I). The single-atomic-configuration approximation was used to compute the molecular energy levels with the l...