Three-dimensional Potential Energy Surface Research Articles

A multi-sheeted three-dimensional potential-energy surface for the H-atom photodissociation of phenol

Extending the previous work of Lan et al. [J. Chem. Phys., 122, 224315 (2005)], a multi-state potential model for the H atom photodissociation is presented. All three "disappearing coordinates" of the departing H atom have been considered. Ab initio CASSCF computations have been carried out for the linear COH geometry of C(2v) symmetry, and for several COH angles with the OH group in the ring plane and also perpendicular to the ring plane. By keeping the C6H5O fragment frozen in a C(2v)-constrained geometry throughout, we have been able to apply symmetry-based simplifications in the constructions of adiabatic model. This model is able to capture the overall trends of twelve adiabats at both torsional limits for a wide range of COH bend angles.

A new ab initio intermolecular potential energy surface and predicted rotational spectra of the Kr−H2O complex

We report a new three-dimensional ab initio intermolecular potential energy surface for the Kr-H(2)O complex with the H(2)O monomer fixed at its experimental averaged structure. Using the supermolecular approach, the intermolecular potential energies were evaluated at the coupled-cluster singles and doubles level with noniterative inclusion of connected triples with the full counterpoise correction for the basis set superposition error and a large basis set including bond functions. The global minimum corresponding to a planar H-bond configuration was located at the intermolecular distance of 3.82 Å with a well depth of 169.98 cm(-1). In addition, two first-order and one second-order saddle points were also identified. The combined radial discrete variable representation∕angular finite basis representation method and the Lanczos algorithm were employed to calculate the rovibrational energy levels for 16 isotopic species of the Kr-H(2)O complexes. The rotational transition frequencies, structure parameters, and nuclear quadrupole coupling constants were also determined for the ground and first intermolecular vibrational excited states and are all in good agreement with the available experimental values.

Collective excitations of Λ hypernuclei

We discuss low-lying collective excitations of Λ hypernuclei using the self-consistent mean-field approaches. We first discuss the deformation properties of Λ hypernuclei in the sd-shell region. Based on the relativistic mean-field (RMF) approach, we show that the oblate deformation for 28Si may disappear when a Λ particle is added to this nucleus. We then discuss the rotational excitations of MgΛ25 using the three-dimensional potential energy surface in the deformation plane obtained with the Skyrme–Hartree–Fock method. The deformation of MgΛ25 is predicted to be slightly reduced due to an addition of a Λ particle. We demonstrate that this leads to a reduction of electromagnetic transition probability, B(E2), in the ground state rotational band. We also present an application of random phase approximation (RPA) to hypernuclei, and show that a new dipole mode, which we call a soft dipole Λ mode, appears in hypernuclei, which can be interpreted as an oscillation of the Λ particle against the core nucleus.

A three-dimensional potential energy surface and predicted infrared spectra for Kr–N2O in the v 1 stretching region of N2O

The three-dimensional ab initio potential energy surface of the Kr–N2O complex was developed at the coupled-cluster single and double with non-iterative treatment of triple excitations [CCSD(T)] level. The potential includes explicit dependence on the symmetric stretching coordinate of the N2O molecule. Two vibrationally averaged potentials with the N2O molecule at both the ground and the first vibrational excited states are generated. Dynamical calculations are performed to determine the bound state energies. The resulting potentials provide a good representation of the experimental data: for 119 infrared transitions of the 84Kr–N2O complex, the root mean square deviation is only about 0.078 cm−1. The predicted rotational constants of the four isotopomers are also in good agreement with their experimental counterparts.

Dynamics of Nitrogen Scattering off N-Covered Ag(111)

We analyze the reflection and adsorption dynamics of N atoms on a (1 × 1) N-covered Ag(111) surface, using an ab initio three-dimensional potential energy surface (3D PES) and classical molecular dynamics (MD) in the frozen and vibrating surface regimes. Our calculations reveal strong changes in the PES upon atomic N adsorption, which becomes much more corrugated than that of the clean Ag(111) surface. This apparently contradicts a key experimental finding made for atoms with incident average energy ⟨Ei⟩ = 4.3 eV, namely that the N reflection dynamics on Ag(111) at N saturation coverage are quantitatively similar to those of clean Ag(111). In good agreement with the experiments, we find that the stronger PES corrugation of the N-covered Ag(111) surface does not affect the angular distribution of the scattered N atoms with that ⟨Ei⟩ value. However, discrepancies are found in the final-to-initial average energy ratios, ⟨Ef⟩/⟨Ei⟩, at grazing outgoing angles. Upon examination of the adsorption trajectories, it can be inferred that gas N is likely to react with adsorbed N. MD shows that this “pickup” mechanism is particularly effective for slow atoms and could be behind the experimental ⟨Ef⟩/⟨Ei⟩ values.

Cold collisions of polyatomic molecular radicals with S-state atoms in a magnetic field: An ab initio study of He + ${\rm CH}_2(\tilde{X})$ CH 2(X̃) collisions

We develop a rigorous quantum mechanical theory for collisions of polyatomic molecular radicals with S-state atoms in the presence of an external magnetic field. The theory is based on a fully uncoupled space-fixed basis set representation of the multichannel scattering wave function. Explicit expressions are presented for the matrix elements of the scattering Hamiltonian for spin-1/2 and spin-1 polyatomic molecular radicals interacting with structureless targets. The theory is applied to calculate the cross sections and thermal rate constants for spin relaxation in low-temperature collisions of the prototypical organic molecule methylene [\documentclass[12pt]{minimal}\begin{document}${\rm CH}_2(\tilde{X}^3B_1)$\end{document} CH 2(X̃3B1)] with He atoms. To this end, two accurate three-dimensional potential energy surfaces (PESs) of the He–\documentclass[12pt]{minimal}\begin{document}${\rm CH}_2(\tilde{X}^3B_1)$\end{document} CH 2(X̃3B1) complex are developed using the state-of-the-art coupled-cluster method including single and double excitations along with a perturbative correction for triple excitations and large basis sets. Both PESs exhibit shallow minima and are weakly anisotropic. Our calculations show that spin relaxation in collisions of CH2, CHD, and CD2 molecules with He atoms occurs at a much slower rate than elastic scattering over a large range of temperatures (1 μK–1 K) and magnetic fields (0.01–1 T), suggesting excellent prospects for cryogenic helium buffer-gas cooling of ground-state ortho-\documentclass[12pt]{minimal}\begin{document}${\rm CH}_2(\tilde{X}^3B_1)$\end{document} CH 2(X̃3B1) molecules in a magnetic trap. Furthermore, we find that ortho-CH2 undergoes collision-induced spin relaxation much more slowly than para-CH2, which indicates that magnetic trapping can be used to separate nuclear spin isomers of open-shell polyatomic molecules.

A three-dimensional potential energy surface and infrared spectra for the Kr–OCS van der Waals complex

The first three-dimensional potential energy surface (PES) of the Kr–OCS complex is developed at the CCSD(T) level with a large basis set plus midpoint bond functions. The potential includes explicit dependence on the v3 antisymmetric stretching coordinate of the OCS molecule. Two vibrationally adiabatic potentials with the OCS molecule at both the ground and the first vibrational v3 excited states are generated. The resulting potentials provide a good representation of the experimental infrared data: for 66 infrared transitions the root-mean-square discrepancy is about 0.011cm−1. The calculated infrared band origin shift, bending ground frequency, and molecular constants associated with the v3 fundamental of OCS are all in better agreement with the experimental counterparts.

Electronic states and rovibrational spectroscopy of the HAlF+ and HAlCl+ cations

Ab initio calculations have been performed to investigate the nature of the low-lying electronic states and the rovibrational energy levels of the electronic ground state of HAlF+ and HAlCl+. The one-dimensional cuts of the low-lying states of both cations have been investigated at the complete active space self-consistent field level, revealing the single-configuration nature of the electronic ground states. Using explicitly correlated coupled-cluster methodology and core-valence basis sets, the three-dimensional potential energy surfaces of both species have then been generated, and the rovibrational energy levels were computed variationally. The analysis of the results reveals the similar nature of the Al–H bond in both species, according to their equilibrium bond lengths and to the Al–H stretching mode frequencies. The rovibrational energy levels of the deuterated isotopologues are also presented.

Theoretical study of the spectroscopically relevant parameters for the detection of HNPq and HPNq (q = 0, +1, −1) in the gas phase

High level ab initio electronic structure calculations at different levels of theory have been performed on HNP and HPN neutrals, anions, and cations. This includes standard coupled cluster CCSD(T) level with augmented correlation-consistent basis sets, internally contacted multi-reference configuration interaction, and the newly developed CCSD(T)-F12 methods in connection with the explicitly correlated basis sets. Core-valence correction and scalar relativistic effects were examined. We present optimized equilibrium geometries, harmonic vibrational frequencies, rotational constants, adiabatic ionization energies, electron affinities, vertical detachment energies, and relative energies. In addition, the three-dimensional potential energy surfaces of HNP(-1,0,+1) and of HPN(-1,0,+1) were generated at the (R)CCSD(T)-F12b∕cc-pVTZ-F12 level. The anharmonic terms and fundamentals were derived using second order perturbation theory. For HNP, our best estimate for the adiabatic ionization energy is 7.31 eV, for the adiabatic electron affinity is 0.47 eV. The higher energy isomer, HPN, is 23.23 kcal∕mol above HNP. HPN possesses a rather large adiabatic electron affinity of 1.62 eV. The intramolecular isomerization pathways were computed. Our calculations show that HNP(-) to HPN(-) reaction is subject to electron detachment.

Prediction of the existence of the N2H− molecular anion

We predict the existence of the N(2)H(-) anion from first principle calculations. We present the three-dimensional potential energy surface and the bound states of the N(2)H(-)/D(-) van der Waals anion. The electronic calculations were performed using state-of-the-art ab initio methods and the nuclear motions were solved using a quantum close-coupling scattering theory. A T-shaped equilibrium structure was found, with a well depth of 349.1 cm(-1), where 18 bound states have been located for N(2)H(-) and 25 for N(2)D(-) for total angular momentum J = 0. We also present the absorption spectra of the N(2)H(-) complex. This anion could be formed after low energy collisions between N(2) and H(-) through radiative association. The importance of this prediction in astrophysics and the possible use of N(2)H(-) as a tracer of N(2) and H(-) in the interstellar medium is discussed.

A new ab initio intermolecular potential energy surface and predicted rotational spectra of the Ne−H2S complex

We report a new three-dimensional ab initio intermolecular potential energy surface for the Ne-H(2)S complex with H(2)S monomer fixed at its experimental average structure. Using the supermolecular approach, the intermolecular potential energies were evaluated at CCSD(T) (coupled cluster with single and double and perturbative triple excitations) level with large basis sets including bond functions. The full counterpoise procedure was employed to correct the basis set superposition error. The planar T-shaped global minimum is located at the intermolecular distance of 3.51 Å with a well depth of 71.57 cm(-1). An additional planar local minimum was found to be separated from the global minimum with an energy barrier of 23.11 cm(-1). In addition, two first-order and one second-order saddle points were also located. The combined radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm were employed to evaluate the rovibrational energy levels for eight isotopic species of the Ne-H(2)S complexes. The rotational transition frequencies for the eight isotopomers were also determined for the ground and first vibrational excited states, which are all in very good agreement with the available experimental values.

POTENTIAL ENERGY SURFACE, MICROWAVE AND INFRARED SPECTRA OF THE Xe–CO2 COMPLEX FROM AB INITIO CALCULATIONS

We present a new three-dimensional potential energy surface for Xe–CO2 including the Q3 normal mode for the υ3 antisymmetric stretching vibration of the CO2 molecule. Two vibrationally adiabatic potentials with CO2 in both the ground (υ3 = 0) and the first excited (υ3 = 1) states are generated by the integration of this potential over the Q3 coordinate. Each potential is found to have a T-shaped global minimum. The radial DVR/angular FBR method and the Lanczos algorithm are employed to calculate the rovibrational energy levels. The calculated band origin shifts, microwave and infrared spectra based on the two averaged potentials are in good agreement with the available experimental data.

Ab initio prediction of vibrational states of the HeCuF helium-containing complex

A global three-dimensional potential energy surface for the HeCuF system, which has a relatively large helium binding energy of ca. 6.2kcal/mol, has been developed using the high-level ab initio CCSD(T) electronic structure method with scalar relativistic effects taken into account. Using the developed potential energy surface, vibrational states of 4HeCuF and 3HeCuF have been calculated quantum mechanically. Spectroscopic detection of these helium-containing complexes has been discussed.

Photodissociation of N2O: Excitation of 1A″ States

We investigate the contributions of the lowest two (1)A" states in the UV photodissociation of N(2)O employing three-dimensional potential energy surfaces and transition dipole moment functions. Because the transition dipole moments are much smaller than for the 2 (1)A' state, we conclude that excitation of the (1)A" states has a marginal effect. The dense vibrational spectrum of the quasi-bound 2(1)A" state possibly explains some of the tiny, noise-like structures of the measured absorption spectrum.

Full dimension Rb2He ground triplet potential energy surface and quantum scattering calculations

We have developed a three-dimensional potential energy surface for the lowest triplet state of the Rb(2)He complex. A global analytic fit is provided as in the supplementary material [see supplementary material at http://dx.doi.org/10.1063/1.4709433 for the corresponding Fortran code]. This surface is used to perform quantum scattering calculations of (4)He and (3)He colliding with (87)Rb(2) in the partial wave J = 0 at low and ultralow energies. For the heavier helium isotope, the computed vibrational relaxation probabilities show a broad and strong shape resonance for a collisional energy of 0.15 K and a narrow Feshbach resonance at about 17 K for all initial Rb(2) vibrational states studied. The broad resonance corresponds to an efficient relaxation mechanism that does not occur when (3)He is the colliding partner. The Feshbach resonance observed at higher collisional energy is robust with respect to the isotopic substitution. However, its effect on the vibrational relaxation mechanism is faint for both isotopes.

The predicted infrared spectrum of the hypermetallic molecule CaOCa in its lowest two electronic states [formula omitted] and [formula omitted

This study of CaOCa is our third paper in a series on Group 2 alkaline-earth M2O hypermetallic oxides. As with our previous calculations for BeOBe and MgOMg, the ab initio calculations we report here show that CaOCa has a linear 1Σg+ ground electronic state and a very low lying linear a˜3Σu+ first excited triplet electronic state. For CaOCa we determine that the singlet–triplet splitting Te(a˜)=386cm-1. We calculate the three-dimensional potential energy surface, and the electric dipole moment surfaces, of each of the two states using a multireference configuration interaction (MRCISD) approach in combination with internally contracted multireference perturbation theory (RS2C) based on full-valence complete active space self-consistent field (FV-CASSCF) wavefunctions with a cc-pwCVQZ-DK basis set for Ca and a cc-pCVQZ basis set for O. We simulate the infrared absorption spectra of 40Ca16O40Ca in each of these electronic states in order to aid in its eventual spectroscopic characterization.

Helium mediated deposition: Modeling the He−TiO2(110)-(1×1) interaction potential and application to the collision of a helium droplet from density functional calculations

This paper is the first of a two-part series dealing with quantum-mechanical (density-functional-based) studies of helium-mediated deposition of catalytic species on the rutile TiO(2)(110)-(1×1) surface. The interaction of helium with the TiO(2)(110)-(1×1) surface is first evaluated using the Perdew-Burke-Ernzerhof functional at a numerical grid dense enough to build an analytical three-dimensional potential energy surface. Three (two prototype) potential models for the He-surface interaction in helium scattering calculations are analyzed to build the analytical potential energy surface: (1) the hard-corrugated-wall potential model; (2) the corrugated-Morse potential model; and (3) the three-dimensional Morse potential model. Different model potentials are then used to study the dynamics upon collision of a (4)He(300) cluster with the TiO(2)(110) surface at zero temperature within the framework of a time-dependent density-functional approach for the quantum fluid [D. Mateo, D. Jin, M. Barranco, and M. Pi, J. Chem. Phys. 134, 044507 (2011)] and classical dynamics calculations. The laterally averaged density functional theory-based potential with an added long-range dispersion interaction term is further applied. At variance with classical dynamics calculations, showing helium droplet splashing out of the surface at impact, the time evolution of the macroscopic helium wave-function predicts that the helium droplet spreads on the rutile surface and leads to the formation of a thin film above the substrate. This work thus provides a basis for simulating helium mediated deposition of metallic clusters embedded within helium nanodroplets.

Energy dissipation channels in the adsorption of N on Ag(1 1 1)

We theoretically study the competition between different energy dissipation channels in the adsorption of N atoms on Ag(111) surfaces. The three-dimensional potential energy surface that describes the interaction between the N atoms and the metal surface is built from density functional theory calculations. Classical dynamics simulations are subsequently performed to evaluate the adsorption probabilities. The contribution of electron–hole pairs excited in the surface during the adsorption process is included in the simulation by an electronic friction coefficient. Phonon excitations are also considered through the Generalized Langevin Oscillator model. We show that the role of the two channels during the adsorption dynamics is very different: phonons are responsible for determining the adsorption probability but electronic excitations are relevant at a later stage to fix the N atoms to the adsorption positions. We conclude that a theoretical model that intrinsically combines both energy dissipation channels is necessary to properly describe the full dynamics of the process.

First principle study of proton transfer in the green fluorescent protein (GFP): Ab initio PES in a cluster model

In this paper we perform high level complete active space self-consistent field (CASSCF) and multi-reference configuration interaction (MRCI) calculations to generate three-dimensional potential energy surfaces for the proton chain transfer in the green fluorescent protein (GFP) based on a minimal quantum mechanical cluster model. Both the electronic ground state and the first excited state are considered within an approximate rigid model. We focus on the energetic terms of the proton transfers in this paper, and the exact quantum dynamics simulations for proton transfer on the ground and excited states will be reported later. Our results from MRCI quantum mechanical calculations are contrasted with those of other computational studies using both CASPT2 method and DFT method, and are compared with the experimental findings for GFP in the full protein environment.

A new ab initio intermolecular potential energy surface and predicted rotational spectra of the Ar−H2S complex

We report a reliable three-dimensional ab initio intermolecular potential energy surface for the Ar-H(2)S complex with H(2)S monomer fixed at its experimental average structure. The potential energies were evaluated using the supermolecular approach at the coupled-cluster level with a large basis set including bond functions. The full counterpoise procedure was used to correct the basis set superposition error. The potential has a planar T-shaped global minimum with a well depth of 177.48 cm(-1) at the intermolecular distance of 3.72 Å. An additional planar local minimum is also found and is separated from the global minimum with an energy barrier with a height of 47.46 cm(-1). The combined radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm were employed to calculate the rovibrational energy levels for three isotopic species of Ar-H(2)S complexes (Ar-H(2)(32)S, Ar-H(2)(33)S, and Ar-H(2)(34)S). The rotational transition frequencies and structural parameters for the three isotopomers were also determined for the ground and the first excited states, which are all in good agreement with the available experimental values.