3D Potential Energy Surface Research Articles

Electronic properties and vibrationally averaged structures of X̃ 2Σ+ MgOH: a computational molecular spectroscopy study.

For X̃ 2Σ+ MgOH, we have calculated the 3D potential energy surface (PES) at the MR-SDCI+Q/[cc-pCV5Z (Mg), aug-cc-pV5Z (O), cc-pV5Z (H)] level and derived the vibrational properties from there using the discrete variable representation (DVR) method. The PES minimum is at the linear structure; hence, MgOH is a "linear molecule." The 3D PES is shallow, and MgOH tends to bend in the region immediately when either or both Mg-O and O-H bonds become longer than those of the equilibrium structure (re(Mg-O) = 1.7614 Å, re(O-H) = 0.9453 Å, and ∠e(Mg-O-H) = 180°). The zero-point structure, determined as the expectation values over the DVR3D wavefunctions, has 〈r(Mg-O)〉0 = 1.7837 Å and 〈r(O-H)〉0 = 0.9948 Å, and the deviation angle from linearity 〈〉0 = 26.4°. The harmonic frequencies ωe for the Mg-O stretching, bending, and O-H stretching modes are 768, 142, and 4060 cm-1, respectively, and the corresponding term values ν1, ν2, and ν3 are 752, 156, and 3867 cm-1. All the vibrational behaviors, such as quasi-linear features, unusual relationship ν2 > ω2, a large amplitude bending motion, etc., are elucidated in terms of the ab initio electronic wavefunctions and the DVR3D vibrational wavefunctions. We have another piece of evidence to support our postulation that a linear molecule is observed as being bent.

Mechanical Efficiency of Photochromic Nanomotors, From First Principles.

Photochromic molecular motors hold promise for a multitude of potential applications in fields ranging from medicine to communications and structural repair. Yet, it is still a challenge to predict their mechanical efficiency. Here, azobenzene is explored as a representative light-driven nanomotor and estimate its quantum yield of photoisomerization and maximum mechanical efficiency. This is based on first-principles mapping of the 3D potential energy surfaces for the ground and excited states of the trans and cis configurations and identifying the minimum energy pathway for isomerization. A work cycle is devised and identifies force constant as the parameter that resembles temperature in the Carnot heat engine, but with very different efficiencies. The results show that the optomechanical efficiency of azobenzene at constant load is about 5% albeit under ideal conditions. To test the hypothesis, the study also explores the optomechanical efficiency of stilbene and 2-butene and shows that their efficiency does not exceed 5%.

Vibrationally unusual behaviors predicted for [XeHXe]+: A computational molecular spectroscopy study

To obtain more evidence for our assertion that the ro-vibrationally averaged structure of a linear molecule is to be observed as being “bent,” we here chose a linear molecule X˜Σg+1 [XeHXe]+.Using the basis sets and calculation level checked against the gas-phase spectroscopy data for XeH+, the 3D potential energy surface (PES) of [XeHXe]+ was calculated at the valence CCSD(T)/[5ZP ANO-RCC (Xe), cc-pV5Z-DK (H)] level. Then, ro-vibrational properties were calculated over the DVR3D wavefunctions derived by the Discrete Variable Representation method.The [XeHXe]+ is a covalently bound, stable cation with 110 kcal/mol of the heat of formation, showing a large amplitude bending motion.Three unusual features are noticed and elucidated. (1) Although the [XeHXe]+ is a linear molecule with re(Xe–H) = re(H–Xe) = 1.8682 Å in D∞h symmetry and the PES is symmetric for the two Xe–H bonds, the r0 structure is unsymmetric with 〈r(Xe–H)〉0 = 1.8881 Å, 〈r(H–Xe)〉0 = 1.9028 Å, and 〈∠(Xe–H–Xe)〉0 = 166.6∘. The 〈∠(Xe–H–Xe)〉0 value of 166.6∘ again confirmed our assertion that a linear molecule is to be observed as being bent. (2) The term value ν3 (846 cm−1, antisymmetric stretching mode) is higher than the harmonic frequency ω3 (820 cm−1), which is unusual since in ordinary molecules νi <ωi (i=1,2,3) due to the anharmonicity. (3) The doubly degenerate bending mode, consisting of a perpendicular motion of the central H atom against the a axis, is anharmonic since this motion is essentially a simultaneous stretching motion of the two Xe–H bonds, which are inherently anharmonic.All these unusual features result from the situation that the (ultra)heavy Xe atoms at both ends stay almost at a standstill during the vibrations, and hence, these three features are specific and characteristic to the [(Ultra)heavy–Light–(Ultra)heavy] atoms system.In addition, from the analysis of the normal modes, the reason is clarified why only the ν1 (symmetric stretching mode) is severely affected by the matrix medium (Tsuge et al.) in the matrix infrared spectroscopy.

Collisional excitation of propargylimine by helium: new ab initio 3D-potential energy surfaces and scattering calculations.

We present quantum coupled-state calculations for the rotational excitation of interstellar propargylimine due to collisions with helium. The calculations are based on new high-accurate three-dimensional potential energy surfaces (3D-PESs) adapted for rigid-rotor scattering computations. The two PESs (Z/E-PGIM-He) were determined using the explicitly correlated coupled-cluster approach with single, double and perturbative triple excitation [CCSCD(T)-F12] and the standard aug-cc-pVTZ basis set. These PESs present many minima with a global minimum of -47.61 cm-1 for Z-PGIM-He and -54.16 cm-1 for E-PGIM-He. While the PESs for both complexes are qualitatively similar, that of E-PGIM-He is more anisotropic. The state-to-state collisional cross-section calculations are performed for all rotational levels J ≤ 12 with energies below Erot = 30 cm-1 and for total energies up to 500 cm-1. The corresponding collisional rate coefficients are derived for kinetic temperatures up to 120 K. A propensity rule is seen, for rotational excitation cross sections and de-excitation rate coefficients, that favors even ΔJ transitions but with different orders of magnitude. We expect that the retrieved results will contribute to improving atmospheric and astrophysics models.

Quantum Dynamical Investigation of Dihydrogen-Hydride Exchange in a Transition-Metal Polyhydride Complex.

The ongoing shift toward clean, sustainable energy is a primary driving force behind hydrogen fuel research. Safe and effective storage of hydrogen is a major challenge (particularly for mobile applications) and requires a detailed understanding of the atomic level interactions of hydrogen with its host materials. The light mass of hydrogen, however, implies that quantum effects are important, so a quantum dynamical treatment is required to properly account for these effects in computational simulations. As one such example, we describe herein the hydrogen exchange dynamics between a hydride and a dihydrogen ligand in the [FeH(H2)(PH3)4]+ model complex. A global three-dimensional (3D) potential energy surface (PES) was constructed by fitting to and interpolating from a discrete set of grid points computed using density functional theory; exact quantum dynamical calculations were then carried out on the 3D PES using discrete variable representation basis sets. Energy levels and their quantum tunneling splittings were computed up to 3000 cm-1 above the ground state. Within that energy range, all three fundamentals have been identified using wave function plots, as well as the first three overtones of the exchange (reaction coordinate) motion and several of its combination bands. From the tunneling splittings, the Boltzmann-averaged tunneling rates were computed. The Arrhenius plot of the total exchange rate shows a clear transition around 150 K, below which the activation energy is essentially zero and above which it is less than half of the electronic structure barrier. This indicates that exchange rates are governed by quantum tunneling throughout the relevant temperature range with the low-temperature regime dominated by a single quantum (ground) state. This work is the first-ever fully quantum dynamical study to investigate the hydrogen exchange dynamics between hydride and dihydrogen ligands coordinated to a transition-metal complex.

Electronic and spin-rovibrational spectroscopy of the HPS+ cation

Using post Hartree-Fock multi-configuration interaction ab initio approaches, the six (four) doublet (quartet) lowest electronic states of thioxophosphane cation, HPS+, are treated. These electronic states are mapped along the internal coordinates, including the HP, PS distances and in-plane HPS bending angle. Several potential minima are located where long-lived HPS+ ions can be found. Also, computations show that the (X˜2A', 12A", 22A", 22A', 14A' and 14A") states are bound, for which we generate their 3D-potential energy surfaces (3D-PESs). After nuclear motion treatments, we determine the rotational and vibrational constants of these states and the pattern of their rovibrational levels up to 4000 cm−1 above the corresponding vibrational ground state level. For instance, the RCCSD(T)/aug-cc-pV(5 + d)Z anharmonic frequencies of HPS+(X˜2A') are computed ν1 = 2237.7, ν2 = 543.0, ν3 = 686.8 (in cm−1). For the lowest electronic excited state (HPS+(12A")), these frequencies change to ν1 = 2330.5, ν2 = 254.6 and ν3 = 749.6 (in cm−1). Several anharmonic resonances are identified. Besides, a very accurate adiabatic ionization energy of HPS (= 9.3173 eV) is deduced using the (U)CCSDT(Q)/aug-cc-pV(T + d)Z approach and where the core-valence (ΔCV), scalar relativistic (ΔSR) and zero point vibrational energy (ΔZPE) corrections are included. Our spectroscopic data should be useful for identifying this ion in laboratory and in media where reactive collisions between PS/PS+ + H+/H or HP/HP+ + S+/S are taking place.

Collision excitation of nitrous acid (HONO) by helium: isomerization effect

ABSTRACTWe generated new 3D-potential energy surfaces (3D-PESs) for the cis-HONO–He and trans-HONO–He weakly bound complexes along the intermonomer coordinates. We used the explicitly correlated Coupled Clusters with single, double, and perturbative triple excitations (CCSD(T)-F12) approach for the electronic structure computations, where the atoms were described using the aug-cc-pVTZ basis set. Then, we derived analytical forms for each PES. These PESs exhibit different shapes and present strong anisotropies. After quantum close-coupling scattering calculations for the lower rotational levels (up to ${9}_{2,7}$), and the coupled-states approximation for higher levels (up to ${22}_{1,22}$) using these PESs, we derived the collisional excitation cross sections of cis-HONO and trans-HONO by He for total energies 0.1 ≤ E ≤ 900 cm−1 and the rate coefficients for kinetic temperatures T ≤ 100 K. Our work shows that the collision data of cis-HONO and trans-HONO are different mainly because of the different 3D-PESs since the rotational energy structures of both isomers are very similar. Also, computations show that the data of the non-detected cis-HONO are as large as those of the detected trans-HONO isomer. They confirm the large values for the detected transition 52,4 → 41,3 of trans-HONO. Therefore, our work strongly suggests revisiting radiative transfer calculations to determine accurately the population of the rotational levels of these isomers. Our work should help astrophysicists for the detectability of such nitrogen oxide molecules and for the possible formation mechanisms and isomerization pathways specificities.

Phosphine interacting with argon: potential energy surface and line widths of PH3 perturbed by Ar.

The phosphine-Ar (PH3-Ar) van der Waals complex's three-dimensional potential energy surface (3D-PES) was mapped along the intermonomer coordinates using the explicitly correlated Coupled Clusters approach. An analytical expansion of this 3D-PES is deduced. The complex characteristics of the intermolecular interactions between PH3 and Ar, which are at the origin of the pressure broadening of the PH3 rovibrational lines, are accurately described by this 3D-PES. Afterwards, the broadening of the phosphine lines perturbed by Ar at room temperature is computed using this 3D-PES. To be able to incorporate this 3D-PES into our collisional broadening computation software, we first modified it with a new "fractional" function. Then, we used the semiclassical Modified Robert and Bonamy model improved by the so-called notion of exact trajectory. For various branches of the ν2 and ν4 PH3 rovibrational bands, room temperature data are provided. Our data agree with the experimental measurements. The precise estimation of PH3 and Ar abundances in planetary atmosphere spectra should benefit greatly from the data provided here.

Relativistic versus Jahn-Teller effects in tantalum and tungsten clusters

We juxtapose the interplay of relativistic and Jahn-Teller effects in small tantalum and tungsten clusters. We employ relativistic techniques to study the low-lying electronic states of Tan for 2 ≤ n ≤ 6. We have used the complete active space MCSCF (CASSCF) techniques for the low-lying electronic states of Ta2 together with DFT techniques including spin–orbit corrections for large clusters that employed relativistic effective core potentials. The results thus obtained were compared with CASSCF/MRCI computations together with the inclusion of spin–orbit coupling for the tungsten trimer. Our computations reveal that unlike clusters containing lighter atoms, the spin–orbit effects overcome Jahn-Teller stabilization effects resulting in more symmetrical structures for tantalum and tungsten clusters. We have also computed the 3D-potential energy surfaces of different interesting regions of the Mexican hat surfaces. Whereas for the trimer and tetramer spin–orbit stabilization seems to overtake Jahn-Teller stabilization, thus resulting in the stabilization of symmetric structures, the Jahn-Teller stabilizations are larger than spin–orbit effects for larger clusters, thus resulting in distorted structures for larger clusters. We have provided a double group and graph-theoretical analysis of the electronic states of tantalum clusters to gain insights into the effect of spin–orbit coupling and pseudorotation on the electronic states of these clusters. The absorption spectra for these clusters are computed using time dependent density functional theory (TDDFT).

Adsorption and Diffusion of Oxygen on Pure and Partially Oxidized Metal Surfaces in Ultrahigh Resolution

The interaction of gas molecules with metal and oxide surfaces plays a critical role in corrosion, catalysis, sensing, and heterogeneous materials. However, insights into the dynamics of O2 from picoseconds to microseconds have remained unavailable to date. We obtained 3D potential energy surfaces for adsorption of O2 on 11 common pristine and partially oxidized (hkl) surfaces of Ni and Al in picometer resolution and high accuracy of 0.1 kcal/mol, identified binding sites, and surface mobility from 25 to 300 °C. We explain relative oxidation rates and parameters for oxide growth. We employed over 150 000 molecular mechanics and molecular dynamics simulations with the interface force field (IFF) using structural data from X-ray diffraction (XRD) and low-energy electron diffraction (LEED). The methods reach 10 to 50 times higher accuracy than possible before and are suited to analyze gas interactions with metals up to the micrometer scale including defects and irregular nanostructures.

New insights into the excited state intramolecular proton transfer (ESIPT) competition mechanism for different intramolecular hydrogen bonds of Kaempferol and Quercetin in solution

In this work, the process of the Excited State Intramolecular Proton Transfer (ESIPT) competition of Kaempferol and Quercetin in methanol was studied by means of the Density Functional Theory (DFT) and the Time-Dependent Density Functional Theory (TDDFT) method. Two different ESIPT reaction pathways were analyzed by the variation trend of the 3D potential energy surfaces (PESs) with the change of the intramolecular hydroxyl bond length through the PESs of the two molecules of the ground state (S0) and the first excited (S1) state. The ESIPT process only occurred between O25–H28 and O22–H28 and was completed within 33.1fs by molecular excited state dynamics simulation. It is demonstrated that when there are two kinds of hydrogen bonds in the molecule, the ESIPT prefers the six-membered ring hydrogen bonds to the five-membered ring hydrogen bonds.

Explicitly correlated potential energy surface of the CH3Cl-He van der Waals complex and applications.

A new 3D-potential energy surface (3D-PES) for the weakly bound CH3Cl-He complex is mapped in Jacobi coordinates. Electronic structure calculations are performed using the explicitly correlated coupled clusters with single, double, and perturbative triple excitations approach in conjunction with the aug-cc-pVTZ basis set. Then, an analytical expansion of this 3D-PES is derived. This PES shows three minimal structures for collinear C-Cl-He arrangements and for He located in between two H atoms, in the plane parallel to the three H atoms, which is near the center of mass of CH3Cl. The latter form corresponds to the global minimum. Two maxima are also found, which connect the minimal structures. We then evaluated the pressure broadening coefficients of the spectral lines of CH3Cl in a helium bath based on our ab initio potential. Satisfactory agreement with experiments was observed, confirming the good accuracy of our 3D-PES. We also derived the bound rovibronic levels for ortho- and para-CH3Cl-He dimers after quantum treatment of the nuclear motions. For both clusters, computations show that although the ground vibrational state is located well above the intramolecular isomerization barriers, the rovibronic levels may be associated with a specific minimal structure. This can be explained by vibrational localization and vibrational memory effects.

Unraveling the stability of cyclobutadiene complexes using aromaticity markers.

Cyclobutadiene (CBD) is the paradigmatic antiaromatic molecule but is known to form highly stable aromatic complexes, e.g. CBD-Fe(CO)3. This intriguing reversal of aromaticity from antiaromatic to aromatic terrain during the complexation process cannot be appropriately handled with single-reference-based theoretical techniques. We explore this aromaticity reversal, for the first time, by a detailed aromaticity analysis using magnetically induced current densities (MICD) and nucleus independent chemical shifts (NICS) using genuine ab initio multi-reference wavefunction-based theory. We trace the dramatic change of aromaticity for a prototypical cyclobutadiene complex, CBD-CH+ (CH+Fe(CO)3), considering a 3D potential energy surface for two independent parameters, namely the approach of CH+ and the automerization cross-section of cyclobutadiene. The 3D potential energy surfaces indicate the presence of a conical intersection/avoided crossing between the ground and the first excited state. The plot of aromaticity indices and the corresponding numerical values show that the change of aromaticity indices is drastic around the conical intersection/avoided crossing and automerization of cyclobutadiene plays a crucial role in the formation of cyclobutadiene complexes. Computations on analogous CBD-Be and CBD-CO systems (Be/COFe(CO)3) emphasize the generality of the conclusions drawn from the CBD-CH+ system.

High-level Ab Initio Studies of the Spectroscopic Properties of Triatomic [Al, S, O]x (x = 0, +1) and Its Potential for Detection in Space

Abstract Highly reliable molecular properties have been computed for the [Al, S, O] x (x = 0, +1) molecular system. Spectroscopic parameters are predicted from analysis of each isomer’s 3D potential energy surface calculated using the explicitly correlated multireference configuration interaction method, including the Davidson correction (MRCI-F12+Q). These parameters provide an accurate prediction of spectroscopic data that can be used in laboratory and observational studies of these molecules. Linear-SAlO is expected to have a large permanent dipole moment suitable for detection in the circumstellar envelopes of large, evolved, oxygen-rich stars such as VY Canis Majoris, IK Tauri, and R Doradus. Frequencies are provided for rotational transitions originating from the most highly populated rotational state based on a Boltzmann distribution. Additionally, both linear isomers exhibit a flat potential along the bending angle and are predicted to have very low bending mode frequencies (&lt;200 cm−1), complicating the spectra of these molecules.

An accurate 5D potential energy surface for H3O+-H2 interaction.

Modeling of the observational spectra of H3O+ allows for a detailed understanding of the interstellar oxygen chemistry. While its spectroscopy was intensively studied earlier, our knowledge about the collision of H3O+ with the abundant colliders in the interstellar medium is rather limited. In order to treat these collisional excitation processes, it is first necessary to calculate the potential energy surface (PES) of the interacting species. We have computed the five-dimensional rigid-rotor PES of the H3O+-H2 system from the explicitly correlated coupled-cluster theory at the level of singles and doubles with perturbative corrections for triple excitations [CCSD(T)-F12] with the moderate-size augmented correlation-consistent valence triple zeta (aug-cc-pVTZ) basis set. The well depth of the PES is found to be rather large, about 1887.2 cm-1. The ab initio potential was fitted over an angular expansion in order to effectively use it in quantum scattering codes. As a first application, we computed dissociation energies for the different nuclear spin isomers of the H3O+-H2 complex.

Dynamics of H(2S) + CH(X2Π) reactions based on a new CH2() surface via extrapolation to the complete basis set limit

A grid of 5285 ab initio points is utilized to construct a 3D potential energy surface (PES) of the system. In the calculation procedure, the aug-cc-pVXZ (X = Q and 5) basis sets with Davidson correction are employed. The reference wave function for the multi-reference configuration interaction calculations is composed of a full valence complete-active-space self-consistent field wave function. In order to get a more accurate PES, the complete basis set (CBS) limit proposal and the many-body expansion form are used, with the total root mean square deviation of the final CBS-PES being 0.0349 eV. Based on the accurate CBS-PES, the stationary points and vibrational energy levels are obtained and examined in detail, which agree well with other theoretical results. Then, utilizing the CBS-PES and quasi-classical trajectory method, the integral cross-sections (ICSs) and rate constants of the → / reactions are calculated. It is found that the present ICSs are in good agreement with other theoretical results, and is the major product channel. For this channel, the rate constants calculated in this work agree well with experimental and other theoretical results in the high-temperature range. It is worth noting that at room temperature, the theoretical results, including the present work, are consistent with each other, but they are all higher (about 7–10 times) than the experimental result, which implies that a new measurement for the rate constant at room temperature is necessary.

New 3D potential energy surface and infrared spectrum of Ar—N2O complex in the N2O v3 fundamental vibration region

The goal of this paper was to re-evaluate 3D potential energy surface of the Ar–N2O complex containing N2O monomer v3 stretching vibrations. Two vibrational potentials for v3 = 0, 1 were obtained and then used to predict infrared spectra and spectroscopic constants of the Ar–N2O complex, which showed excellent agreement with the experimentally obtained infrared spectra.

New calculations of five-dimensional fission barriers for actinide nuclei

New calculations of fission barrier heights in a five-dimensional (5D) deformation space for actinide nuclei have been performed based on a macro-microscopic (MM) model. To calculate potential energy surface (PES), we use the 5D generalized Lawrence shape (GLS) realistic parameterization as the shape description, the Lublin-Strasbourg Drop (LSD) model for the macroscopic energy and the folded-Yukawa model as the single-particle potential. A method to use two-center oscillator basis in calculating Hamiltonian matrix on any kind of shape description was presented. For the pairing energy, we use the SBCS model. Finally, Strutinsky method is used to calculate the microscopic correction energy. To find the fission barriers and fission paths, some concepts, such as basins, edges and neighbors from geography, are extended to identify the topographical structures on the 5D PES and we assume that the fission path follows the line of steepest descent. The fission barriers and double-humped paths of U and Pu isotopes are calculated.

Collisional excitation of NH(3Σ-) by Ar: A new ab initio 3D potential energy surface and scattering calculations.

Collisional excitation of light hydrides is important to fully understand the complex chemical and physical processes of atmospheric and astrophysical environments. Here, we focus on the NH(X3Σ-)-Ar van der Waals system. First, we have calculated a new three-dimensional Potential Energy Surface (PES), which explicitly includes the NH bond vibration. We have carried out the ab initio calculations of the PES employing the open-shell single- and double-excitation couple cluster method with noniterative perturbational treatment of the triple excitations. To achieve a better accuracy, we have first obtained the energies using the augmented correlation-consistent aug-cc-pVXZ (X = T, Q, 5) basis sets and then we have extrapolated the final values to the complete basis set limit. We have also studied the collisional excitation of NH(X3Σ-)-Ar at the close-coupling level, employing our new PES. We calculated collisional excitation cross sections of the fine-structure levels of NH by Ar for energies up to 3000 cm-1. After thermal average of the cross sections, we have then obtained the rate coefficients for temperatures up to 350 K. The propensity rules between the fine-structure levels are in good agreement with those of similar collisional systems, even though they are not as strong and pronounced as for lighter systems, such as NH-He. The final theoretical values are also compared with the few available experimental data.

AN INSILCO STUDY OF 1,1-DIFLUORO-2-METHOXYPROPANE REACTION MECHANISM WITH THE BROMINE MONOXIDE (BrO) RADICAL

An Insilco study was carried out on the thermochemistry, mechanism and kinetics of the Hydrogen abstraction reaction of 1,1-difluoro-2-methoxypropane (CH 3 CH(OCH 3 )CHF 2 ) with the Bromine monoxide radical (BrO) using the Density Functional Theory (DFT) based M06-2X/ 6-311++G ** method. The energy values were immediately improved via optimization at DFT/M06-2X/6-311++G(2df,2p) level ( single-point calculations) of the reacting species involved. The Monte Carlo search on the investigating hydrofluoroether (HFE) showed nine conformers with the lowest global minimum conformer being predicted and considered for this work. The results of this study showed that the atmospheric oxidation reaction of CH 3 CH(OCH 3 )CHF 2 with the BrO radical proceeded in four (4) plausible reaction routes. The total experimental rate of 4.34*10 -06 cm -3 molecule -1 sec -1 for HFE + BrO reaction was estimated with atmospheric lifetime (ALT)/global warming potential (GWP) of 1.80 years and 165.30 respectively. The 3D potential energy surfaces (PES) for the reaction was however constructed at absolute temperature of 298.15 K.