Wave Packet Propagation Method Research Articles

Quantum dynamical study on 15N ＋ 14N14N isotope exchange reactions at high energies

In this study, we conduct quantum dynamical calculations at relatively high energies on the exchange reaction 15N ＋ 14N14N →15N14N ＋ 14N on its ground electronic N3 (4A′′) potential energy surface (PES) utilizing the time-dependent wave packet (TDWP) propagation method. Our primary focus is on analyzing the reaction mechanism for 15N ＋ ortho-14N14N (j = 0) and para-14N14N (j = 1) cases. We also explore the influence of varying J (up to 120) of the three-body system and the initial vibrational level (ν = 1, 5, 10) of the diatom on the reaction probability (RP) for ortho and para configurations.

Theoretical study of resonant charge exchange between H−ion and adsorbate-covered metal surface Cu(111)/Cu(110) with adsorbates Li+/Na+

The influence of the surface type on resonant charge exchange between H−ion with a metal surfaces Cu(111) and Cu(110) covered by adsorbate Li+/Na+has been studied. A model static problem was considered. For modeling, athree-dimensional realization of the wave-packet propagation method was used. The Cu(110) andCu(111) surfaces were described by a pseudopotential, derived from a density functional theory (DFT).An occupation of H− ion, an electron density dynamics and an ion level width were analyzed. As aresult, we obtained that an electron oscillates more in case of the surface Cu(111). Furthermore, the resonant charge exchange is more efficient for Cu(111) surface.

Photodissociation dynamics and UV absorption spectrum of acetone oxide (CH3)2COO.

The photodynamics and B1A' ← X1A' absorption spectrum of acetone oxide, (CH3)2COO, are studied theoretically from first principles. The underlying adiabatic potential energy curves (and surfaces) are computed by a second-order multireference perturbation theory method and diabatized using a diabatization by ansatz scheme. To confirm the results, for selected geometries EOM-CCSD and XMS-RS2C calculations were also performed. The dynamical calculation rests on the multi-configuration time-dependent Hartree wavepacket propagation method. The experimental absorption spectrum is reproduced satisfactorily. This result serves to validate the Hamiltonian model built within the quasi-diabatic representation. Contrary to the smallest Criegee intermediate, CH2OO, it is found that the vibronic coupling between the B and C states of (CH3)2COO plays an essential role in reproducing the experimental absorption spectrum. Time-dependent electronic populations reveal a faster decay than for the smaller system CH2OO. This is interpreted in terms of the stronger coupling between the B and C states in the larger system leading to a shorter lifetime for the B state than in CH2OO.

Elucidation of vibronic structure and dynamics of first eight excited electronic states of pentafluorobenzene.

Vibronic coupling in the first eight electronic excited states of Pentafluorobenzene (PFBz) is investigated in this article. In particular, the vibronic coupling between the optically bright ππ* and optically dark πσ* states of PFBz is considered. A model 8 × 8 diabatic Hamiltonian is constructed in terms of normal coordinate of vibrational modes using the standard vibronic coupling theory and symmetry selection rule. The Hamiltonian parameters are estimated with the aid of extensive ab initio quantum chemistry calculations. The topography of the first eight electronic excited states of PFBz is examined at length, and multiple multi-state conical intersections are established. The nuclear dynamics calculations on the coupled electronic surfaces are carried out from first principles by the wave packet propagation method. Theoretical results are found to be in good accord with the available experimental optical absorption spectrum of PFBz.

Local effects during ion scattering on adsorbate-covered surfaces

This study addresses the importance of adsorbate-induced local effects during collisions between projectiles and adsorbate-covered surfaces. Various systems are investigated: H− on Na/Ag(111); H− on Na/Cu(111); and Li+ on K/Al(100), by using wave packet propagation methods. From the projectile's perspective, the adsorbate's presence on the surface can be felt from up to a few tens of atomic units away when the projectile is close to the surface, and up to 100 a.u or more when the projectile is on top of adsorbate. This is a well-defined bell-shape region around the adsorbate. However, the scattered ion/neutral fractions are not significantly affected unless the projectile impacts the surface in the close 10–15 a.u. vicinity of the adsorbate. Scattering from adsorbate sites compared to scattering from substrate sites produces very different ion/neutral fractions, that vary not only with the surface coverage, but especially with the distance from the projectile's point of impact on the surface to the adsorbate. Our calculated Li neutral fractions obtained after scattering Li+ from K/Al(100) are in satisfactory agreement with the experimental results.

Distinctive onset of electron correlation in molecular tautomers

We investigate the attosecond response of the electronic cloud of a molecular system to an outer-valence ionization. The time needed for the remaining electrons to respond to a sudden perturbation in the electronic structure of the molecule is a measure of the degree of electron correlation. Using the ab initio multielectron wave-packet propagation method, we show that this response time can be sensitive to the molecular structure and the symmetry of the ionized molecular orbital. Our analysis revealed differences in the temporal signatures of ultrafast charge migration processes in the context of tautomeric hydrogen in multinuclear systems, and the relevance of distinctive onset of electron correlation within the overall molecular complexity.

Time-dependent quantum wave packet calculation for reaction S−(2P)+H2(1Σg+)→SH−(1Σ)+H(2S) on ab Initio potential energy surface

The time-dependent wave packet propagation method was applied to investigate the dynamic behaviours of the reaction S−(2P)+H2(1Σg+)→SH−(1Σ)+H(2S) based on the electronic ground state (2A′) potential energy surface of the SH2− ionic molecule. The collision energy dependent reaction probabilities and integral cross sections are obtained. The numerical results suggest that there are significant oscillation structures over all the studied range of the collision energies. The vibrational excitation and rotational excitation of the diatomic reagent H2 promote the reactivity significantly as suggested by the numerical total reaction probabilities with the initial rotational quantum number of j = 0, 2, 4, 6, 8, 10, and the vibrational quantum number v = 0, 1, 2, 3, 4. The numerical integral cross sections are quite consistent with the experimental data reported in previous work.

Efficient numerical method for evaluating normal and anomalous time-domain equilibrium Green's functions in inhomogeneous systems

In this work we develop EPOCH: Equilibrium Propagator by Orthogonal polynomial CHain, a computationally efficient method to calculate the time-dependent equilibrium Green's functions, including the anomalous Green's functions of superconductors, to capture the time-evolution in large inhomogeneous systems. The EPOCH method generalizes the Chebyshev wave-packet propagation method from quantum chemistry and efficiently incorporates the Fermi-Dirac statistics that is needed for equilibrium quantum condensed matter systems. The computational cost of EPOCH scales only linearly in the system degrees of freedom, generating an extremely efficient algorithm also for very large systems. We demonstrate the power of the EPOCH method by calculating the time-evolution of an excitation near a superconductor-normal metal interface in two and three dimensions, capturing transmission as well as normal and Andreev reflections.

H− ion fractions scattered from Ag(111) and polycrystalline Ag

Experimental H− ion fractions measured after H− scattering from Ag(111) and polycrystalline Ag at 1 keV incident energy in specular conditions revealed a larger ion fraction on H−/Ag(111) compared to polycrystalline Ag for exit angles less than 100 measured from surface, while a smaller ion fraction has been obtained on H−/Ag(111) compared to polycrystalline Ag for exit angles larger than 100. The H− ion fractions on Ag(111) are calculated with the Wave Packet Propagation method adapted to ion-surface interactions. The calculated ion fractions nicely reproduce the experimental results. A detailed study based on the analysis of the projected density of states for various ion-surface distances, the ion's interaction time with the surface, and the ion's distance of closest approach to surface, explains the behaviour of ion fractions on Ag(111) and polycrystalline Ag at small and large exit angles. At small angles, the effect of a larger distance of closest approach dominate over the ion's interaction time with the surface. This translates into less ion decay on Ag(111), because the states correlated asymptotically with H− and the surface state do not fully go through their avoided crossing and are mostly located inside the band gap. At larger angles, the ion is getting closer to the surface and the two states fully go through the avoided crossing. The state correlated asymptotically with H− moves into the image states energy region, while the state correlated asymptotically with the surface state approaches the bottom of the band gap. The electron loss is significant, and translates into a reduced ion survival on Ag(111).

Electronic decay through non-linear carbon chains

A multielectron wave-packet propagation method was used to calculate the electronic decay of oxygen and fluorine 2s vacancies for a group of trifluoroalkyl alcohols, HOCnH(2n−1)F3, with n between 1 and 5. Whether ionizing O2s or F2s orbitals, it is shown that an electron can be emitted non-locally from the opposite terminus of the molecule. The decay of the O(2s−1) state is found to be about 2–3 times faster than that of the F(2s−1), but in both cases the process takes only a few femtoseconds, demonstrating a highly efficient energy transfer through the carbon bridge. A comparison to the previously reported non-local decay in linear difluorocumulenone systems shows that the non-linearity of the trifluoroalkyl alcohols does not appear to dramatically influence the decay efficiency. These results shed light onto the nature of the scaling of electron correlation and open the door to the potential design of molecules that take advantage of this mechanism.

Some Features of the Electron Exchange between Ions and a Metal Surface Caused by its Atomic Structure

Some features of the electron exchange between ions and a metal surface caused by its atomic structure are studied. The simulation is based on three-dimensional implementation of the wave-packet propagation method using pseudopotentials describing the metal at the atomic level. Three-dimensional pseudopotentials for the Cu(100), Cu(110), and Cu(111) surfaces, which reproduce well-known electron-exchange regularities well, are constructed using density functional theory. When considering the model “static” problem, it is shown that the lateral position of an ion weakly affects the main characteristics of the electron exchange and ion propagation along one of the directions in the crystal. However, three-dimensional pseudopotentials taking the atomic structure of the metal into account make it possible to obtain a more realistic picture of the electron transition than widely used one-dimensional model pseudopotentials. For example, when simulating grazing scattering with the use of one-dimensional pseudopotentials, the electron retains the parallel velocity component after the passing to the metal, which is contrary to fact. If three-dimensional potentials are used, then the parallel component of the electron velocity in the metal decreases, which is more correct.

Effect of initial vibrational excitation on the methane cation sub-femtosecond photodynamics

An ab initio ab quantum dynamics study is attempted to understand the effect of initial vibrational state excitation on the sub-femtosecond photodynamics of the methane cation. A time-dependent wave packet (WP) propagation method is utilised where the WPs are prepared for each initial vibrational state of the neutral species of the title cation and its deuteriated isomer. The ratio of the squared of the nuclear autocorrelation functions (ACFs) of CD and CH on the lowest potential sheet of the state are calculated in full dimensionality, including nonadiabatic coupling of the three electronic sheets. The results predict the above ratio to start at unity and then increase with time before passing through a maximum, irrespective of the initial vibrational state. At the first maximum, such a ratio is found to decrease with the number of nodes of the vibrational wave function while the magnitudes of the ACFs of CD and CH diminish gradually with vibrational excitation. This is enhanced by inclusion of further excited vibrational modes. The present results indicate that nuclear motion on the lowest adiabatic sheet of the states of title cation can be slowed down by initial vibrational state excitation.

The role of vibronic coupling in the electronic spectroscopy of maleimide: a multi-mode and multi-state quantum dynamics study.

The first two excitation bands below 7 eV in the electronic absorption spectrum of maleimide are investigated using a model Hamiltonian including four low-lying singlet excited states within the manifold of 24 vibrational modes. The role of non-adiabatic effects is studied and shines light on both the broad, inter-state coupling-dominated spectral band as well as the fine-structured, not-so-strong coupled band. Calculations have been performed using the Multiconfigurational Time-Dependent Hartree (MCTDH) wavepacket propagation method as well as its multilayer version (ML-MCTDH) using a quadratic vibronic coupling (QVC) Hamiltonian model where parameters are obtained from fitting adiabatic potential energy surfaces computed by ab initio methods. The quantum dynamics calculations provide information on the relaxation dynamics and the vibrational modes involved. Already with a low-order vibronic coupling model and only a few modes being considered, a quantitative agreement with the experimental spectrum is obtained. However, it is found that all modes need to be considered to get a full picture of the photo-excited relaxation dynamics of this molecule.

Novel potential energy surface-based quantum dynamics of ion–molecule reaction **Project supported by the National Natural Science Foundation of China (Grant Nos. 11674198 and 11304185).

According to a novel electronic ground-state potential energy surface of , we calculate the reaction probabilities and the integral cross section for the titled reaction by the Chebyshev wave packet propagation method. The reaction probabilities in a collision-energy range of 0.0 eV–1.0 eV show an oscillatory structure for the reaction due to the existence of the potential well. Compared with the results of Martínez et al., the present integral cross section is large, which is in line with experimental data.

Curvature effects on the electronic and transport properties of semiconductor films

Within the effective mass approximation, we study the curvature effects on the electronic and transport properties of semiconductor films. We investigate how the geometry-induced potential resulting exclusively from periodic ripples in the film induces electronic confinement and a superlattice band structure. For fixed curvature parameters, such a confinement can be easily tuned by an external electric field, hence features of the superlattice band structure such as its energy gaps and band curvature can be controlled by an external parameter. We also show that, for some values of curvature and electric field, it is possible to obtain massless Dirac bands for a smooth curved structure. Moreover, we use a wave packet propagation method to demonstrate that the ripples are responsible for a significant inter-sub-band transition, specially for moderate values of the ripple height.

H2/LiF(001) diffractive scattering under fast grazing incidence using a DFT-based potential energy surface

Grazing incidence fast molecule diffraction (GIFMD) has been recently used to study a number of surfaces, but this experimental effort has not been followed, to present, by a subsequent theoretical endeavor. Aiming at filling this gap, in this work, we have carried out GIFMD simulations for the benchmark system H 2 /LiF(001). To perform our study, we have built a six-dimensional potential energy surface (6D-PES) by applying a modified version of the corrugation reducing procedure (CRP) to a set of density functional theory (DFT) energies. Based on this CRP interpolated PES, we have conducted quantum dynamics calculations using both the multiconfiguration time-dependent Hartree and the time-dependent wave packet propagation methods. We have compared the results of our GIFMD simulations with available experimental spectra. From this comparison, we have uncovered a prominent role of the interaction between the quadrupole moment of H 2 and the electric field associated with LiF(001) for specific incidence crystallographic directions. We show that, on the one hand, the molecule's initial rotation strongly affects its diffractive scattering and, on the other hand, the scattering is predominantly rotationally elastic over a wide range of incidence conditions typical for GIFMD experiments.

Effect of internal excitations of reagent diatom on initial state-selected dynamics of C + OH reaction on its second excited (14A″) electronic state

ABSTRACTInitial state-selected total reaction probabilities and integral reaction cross sections (ICSs) of, C(3P) + OH (X2Π) → CO(a3Π) + H (2S), reaction on its second excited electronic state (14A″) are calculated with the aid of a time-dependent wave packet propagation method within the coupled states approximation. Partial wave contributions for the total angular momentum quantum number, J=0–48, were necessary to obtain converged ICSs for OH (v=0, j=0) upto a collision energy of ∼0.25 eV. In case of rotationally and vibrationally excited OH, many more partial wave contributions had to be included. Dense oscillatory structures are found in total reaction probabilities due to the formation of quasibound collision complexes inside the wells (of depth ∼2.25 eV and ∼1.85 eV) present on the potential energy surface. While reagent vibrational excitation promotes the reaction, no such general trend is found with rotational excitation. The results of the present study are compared with the literature data. Mechanistic details of the C + OH reaction occurring on its ground, first and second excited electronic states are compared and discussed.

Dynamics and resonances of the H(2S) + CH+(X1Σ+) reaction in the electronic ground state: a detailed quantum wavepacket study.

Initial state-selected and energy resolved channel-specific reaction probabilities, integral cross sections and thermal rate constants of the H(2S) + CH+(X1Σ+) reaction are calculated within the coupled states approximation by a time-dependent wave packet propagation method. The new ab initio global potential energy surface (PES) of the electronic ground state (1 2A') of the system, recently reported by Li et al. [J. Chem. Phys., 2015, 142, 124302], is employed for this purpose. All partial wave contributions up to the total angular momentum J = 60 are considered to obtain the converged integral reaction cross section up to a collision energy of 1.0 eV. Thermal rate constants are calculated by averaging the reaction cross sections over the Boltzmann distribution of energies and compared with the available theoretical and experimental results for the temperature range 10-1000 K. Investigation of the channel-specific reaction attributes shows that the H abstraction (CH+ destruction) channel is highly favored over the H exchange channel. The effect of rotational and vibrational excitations of the CH+ reagent on the dynamics is also studied. The resonances formed during the course of the reaction are also identified by calculating the transition state spectrum and characterized in terms of the eigenfunctions and lifetimes. More than 260 vibrational levels are obtained and their eigenfunctions are calculated, which are represented in terms of the nodal assignments and the eigenenergies. They reveal both the local and hyperspherical behavior for the bound and quasibound states of the CH2+ complex in the ground 1 2A' surface. The lifetime analysis of the quasibound states indicates that the CH2+ resonances survive for as long as ∼400 fs at high energies (E ∼ 2.0 eV) and are expected to decay faster with further increasing energy. Finally, the type of mechanism for the formation of the product (C+ + H2) is elucidated.

Electronic decay through carbon chains

Using the multielectron wave-packet propagation method the electronic decay of O2s vacancy in fluorinated cumulenones, OCnF2, containing a chain of up to five carbons is traced in time and space. It is shown that in all studied cases this state decays non-locally by emitting an electron from the remote fluorines. Even in the pentatetraenone case, where the oxygen and the flourines are more than 7Å apart, this non-local decay is extremely efficient, with a time constant of about 5fs. The process can be viewed as an ultrafast energy transfer through the carbon chain and thus our systematic study allows to shed some light on the dependence of the time scale of the electron-correlation driven energy transfer through a medium.

Quantum wavepacket dynamics of the N([formula omitted]) + NO([formula omitted]) reaction and its isotopic variants: Integral cross sections and thermal rate constants

We investigate the initial state-selected dynamics of the title reaction on its ground (1 3A″) and first excited (1 3A′) triplet potential energy surfaces (PESs) by a time-dependent wavepacket propagation method, employing the ab initio analytical PESs developed by Gamallo et al. (2003). All partial wave contributions up to the total angular momentum J=140 are found to be necessary for the scattering of NO diatom in its vibrational and rotational ground state up to a collision energy ∼0.9eV. The converged initial state-selected reaction attributes viz., reaction probabilities, integral cross sections and thermal rate constants are obtained within the centrifugal sudden (CS) approximation and the convergence of the results are carefully checked by varying all parameters used in the numerical calculations. The dynamical results are compared with the other reported theoretical and experimental findings. Investigation on the energy-resolved channel-specific reaction probabilities infers that the N2 formation channel is very much favorable than the N-exchange channel. The reaction proceeds via some metastable resonances, observed from the oscillatory probability curves, which is more in the latter channel compared to the former. The effect of rotational and vibrational excitations of the reagent (NO diatom) on the dynamics is examined. We also examine the effect of isotopic substitution of N-atom (14N by 15N) on the reaction dynamics.