Time-dependent Wave Packet Method Research Articles

The global potential energy surface of the RbH2 system and dynamics studies of the H + RbH → Rb + H2 reaction

A new global potential energy surface of the ground state of the RbH2system is constructed by using the permutation invariant polynomial neural network method.In the ab initiocalculations, the aug-cc-pVQZ basis set for H, Def2-QZVPP basis set for Rb, and multi-reference configuration interaction method with Davidson correction are used. The topographical features of the new PES are discussed in detail, and no wells and barriers in the minimum energy path are found. Thereafter, specific initial-state dynamics calculations of the H + RbH (v = 0 ∼ 2,j = 0) → Rb + H2reaction are carried out based on the new PES by means of the time-dependent quantum wave packet method with a second-order split operator. The dynamics results indicate that the vibrational excitation of RbH molecules reduces and increases the reaction probability when the collision energy is below 0.4 eV and above 0.4 eV, respectively.

Time-dependent wave packet dynamics study of the resonances in the H + LiH+(v = 0, j = 0) → Li+ + H2 reaction at low collision energies.

The depletion process of LiH+ by H collision plays an important role in the evolution of the early universe and astrophysical processes, including the eventual charge-states, abundances of atomic and molecular species and ensuing astrochemistry. Here, a quantum dynamics study on the H + LiH+(v = 0, j = 0) → Li+ + H2 reaction is performed at the low collision energy range from 0.1 meV to 10 meV using the time-dependent wave packet method. A Feshbach resonance peak is observed near 0.8 meV collision energy on the total reaction probability curves. This resonance originates from the coupling with the v = 0, j = 1 energy level of the reactant LiH+, and it is dominated by the contributions of J = 0-4 partial waves. Another partial wave resonance is also found on the total integral cross section at 1.2 meV, which is closely connected to the opening of the J = 7 partial wave. The opening of the J = 7 partial wave generates a notable forward scattering peak, and the Feshbach resonance can promote both the forward and backward scatterings. Moreover, the total and product vibrational state-resolved rate coefficients for the temperature range of 1-100 K are also reported.

Non-adiabatic couplings induced complex-forming mechanism in H+MgH+ → Mg++H2 reaction

A chemical process may involve multiple adiabatic electronic states, and non-adiabatic couplings play an important role in the reaction mechanism. In this work, the effect of non-adiabatic couplings in the H+MgH+ → Mg+ + H2 reaction are studied using the time-dependent wave packet method and trajectory surface hopping method. The calculated results show that the reaction follows a direct abstraction process when the non-adiabatic couplings are neglected. However, when non-adiabatic couplings are included in the calculations, a long-lived excited state complex (MgH2+)* can be formed during the reaction. These direct and complex-forming reaction pathways are revealed by trajectory surface hopping calculations. The non-adiabatic couplings induced complex-forming mechanism not only increases the reactivity but also has significant effect on the product vibrational state distribution.

An accurate many-body expansion potential energy surface for SiH2 (11 A') using a switching function formalism.

An accurate many-body expansion potential energy surface for the ground state of SiH2 is reported. To warrant the correct behavior at the Si (1D) + H2 (X1Σ+g) dissociation channels involving silicon in the first excited Si (1D) and ground Si (3P) states, a switching function formalism has been utilized. A great deal of ab initio points based on aug-cc-pV(Q+d)Z and aug-cc-pV(5+d)Z basis sets are utilized at the multi-reference configuration interaction level using the full-valence-complete-active-space wave function as the reference. Subsequently the calculated energies are corrected via a many-body expansion method to extrapolate to the complete basis set limit. The topographic features of the novel many-body expansion global potential energy surface are studied in detail, showing a good agreement with the theoretical and experimental results in the literature. Moreover, the integral cross-section of the Si (1D) + H2 (X1Σ+g) → H (2S) + SiH (X2Π) reaction has been calculated using the time-dependent wave packet method, which provides support for the reliability of the title potential energy surface. This work can serve as the foundation for the study of Si (1D) + H2 (X1Σ+g) reaction kinetics, and for the construction of the larger multibody expansion potential energy surface of silicon/hydrogen containing systems.

Quantum dynamics study of OH−+CH3I reaction: Reaction probability, integral cross section, and energy efficacy

We investigate the reaction probability, integral cross section, and energy efficiency of the OH−+CH3I reaction using the time-dependent quantum dynamics wave packet method. A four-degree-of-freedom dynamics model is developed for this study due to the synchronized SN2 bond-breaking and formation mechanism. We find that the reaction probability decreases as a function of the collision energy, which is a typical character of reactions with a negative energy barrier. The ground-state integral cross section calculated using this model is in excellent agreement with the quasi-classical trajectory results. The integral cross-section ratios of the vibrational excitations over the ground state, at the same equal amount of total energy, indicate that the vibrational motion of the CH3–I is more efficient in enhancing the reactivity than the translational motion, which, in turn, has a bigger contribution to the reactivity than the C–H3 vibrational motion. The energy efficacy order in the reactivity is confirmed by the sudden vector model prediction.

An accurate NH2(X2A'') CHIPR potential energy surface via extrapolation to the complete basis set limit and dynamics of the N(2D) + H2(X1Σ+g) reaction.

The amidogen radical (NH2) and its associated N(2D) + H2(X1Σ+g) → H(2S) + NH(X3Σ-) reaction have great significance in interstellar chemistry and the accurate potential energy surface (PES) is the basis for studying them. We report a new and accurate PES for the ground state NH2(X2A'') using the combined-hyperbolic-inverse-power-representation methodology based on 7970 ab initio energy points computed at the Davidson-corrected internally contracted multireference configuration interaction level of theory. Both aug-cc-pVTZ and aug-cc-pVQZ basis sets have been employed to extrapolate the energies to the complete basis set limit. The analytical PES reproduces well with the ab initio energy points with a root mean square deviation of 55.7 cm-1. The topographical features of the analytical PES are examined in detail and agree well with the previous theoretical results. The integral cross sections and rate constants of the N(2D) + H2(X1Σ+g) → H(2S) + NH(X3Σ-) reaction are obtained using the quasi-classical trajectory method and the time-dependent wave packet method and then compared with the available theoretical and experimental values.

Ten-dimensional quantum dynamics study of H+CH3D → H2+CH2D reaction

The mode selectivity of the H+CH3D→H2+CH2D reaction was studied using a recently developed ten-dimensional time-dependent wave packet method. The reaction dynamics are studied for the reactant CH3D initially from the ground state, the CH3 symmetry and asymmetry stretching excitation, the CD stretching excitation and the fundamental and the first overtone of the CH3 bending mode. The calculated reaction probabilities show that exciting either of the CH3 stretching modes enhances the reactivity in the collision energy range below 1.0 eV, while the CD stretching excitation does not obviously prompt the reaction. Fundamental CH3 bending excitation has nearly no effect on promoting reactivity. However, a significant enhancement is observed for the first overtone excitation of the CH3 bending mode, resulting from the Fermi resonance between the fundamental state of the CH3 symmetry stretching mode and the first overtone state of the CH3 bending mode.

Dynamic study of the D + DAu reaction based on a new ground potential energy surface

Based on the ground potential energy surface (PES) (2A') constructed by Yuan and coworkers, the D + DAu reactive scattering was investigated using the time-dependent wave packet method. It was found that the total reaction probabilities and integral cross section of the D + DAu reaction are smaller than those of the H + HAu reaction, due to smaller zero point energy and weaker tunneling effect. The abstract and exchange reaction channel exhibit different reaction mechanisms, a direct reaction mechanism in the abstract channel and long lifetime indirect mechanism in the exchange channel, respectively. During the reaction, the collision energy could be efficiently transferred to vibration of the D2 product in the abstract reaction channel and rotation of the DAu product in the exchange channel.

State-to-state quantum dynamical study of H + Br2 → HBr + Br reaction

The time-dependent wave packet method has been employed to calculate the state-to-state integral cross sections and differential cross sections (DCSs) for three initial states of the title reaction on the recently constructed neural network potential energy surface. It is found that the product HBr(υ′ = 2, 3, 4) states have the dominated population in the entire energy region considered here, indicating an inverted HBr vibrational state distribution. More than half of the available energy ends up as product internal motion, and most of which goes into the vibrational motion. Our calculations show that initial rotational excitation of Br2 has little effect on the product ro-vibrational state distributions and DCSs of the reaction. While the initial vibrational excitation has some influences. The initial vibrational excitation to υ0 = 5 obviously enhance the product vibrational excitation in the low energy region. The DCSs for collision energy up to 0.5 eV at the ground and rotationally excited state are peaked in the backward direction, but the width of the angular distribution increases considerably with the increase of collision energy. For the vibrationally excited state, the DCSs are rather complicated with some strong forward scattering peaks for highly vibrationally excited products.

Calculating the S -matrix of low-energy heavy-ion collisions using quantum coupled-channels wave-packet dynamics

We investigate the fusion and scattering of a $^{16}\mathrm{O}$ projectile on $^{152,154}\mathrm{Sm}$ targets using the time-dependent coupled-channels wave-packet method. We benchmark calculations of the $S$-matrix elements, fusion cross sections, and scattering differential cross sections with those from the time-independent coupled-channels method, and compare the results to experimental data. We find that our time-dependent method and the time-independent method produce quantitatively similar results for the $S$-matrix elements and fusion cross sections, but our method cannot quantitatively explain the experimental scattering differential cross sections, mainly due to the low maximum number of partial waves produced by the time-dependent method. Nevertheless, the strong agreements between our method and the time-independent method demonstrates that the time-dependent coupled-channels wave-packet method can be used to address fusion reactions for a wide range of energies, with the advantage of being able to extend to time-dependent Hamiltonians for more advanced modeling of nuclear reactions.

Control of molecular-field-free orientation steered by asymmetric phase-jump laser pulses

• The molecular orientation with phase-jump laser pulse is investigated by time-dependent quantum wave packet method. • The asymmetry of laser pulse has a significant influence on the orientation. • The molecular orientation is effected by the laser pulse parameters. A theoretical scheme used for manipulating the orientation of LiH molecules with phase-jump laser pulse is proposed. The time-dependent quantum wave packet method is used to numerically compute the wave-function of molecules by including both vibrational and rotational degrees of the freedom. The effect of asymmetric phase jump pulses on molecular orientation can be well understood by a train of HCPs kicking the molecule. The effective orientation of molecules can be achieved by phase-jump laser pulse. The maximal orientation degree, 0.757, and the longest orientation duration, 0.365 ps, are given by optimizing the parameters of phase-jump laser pulse. The molecular orientation is influenced significantly by phase and phase-jump time. Also the molecular orientation is dependent on pulse frequency, peak intensity and system temperature.

Non-adiabatic quantum dynamics studies of the Mg+(3p) + D2 → MgD+ + D reaction

Non-adiabatic quantum dynamics study of the Mg + (3p) + D 2 reaction was carried out by using the time-dependent wave packet method. The results show that there is the triatomic complex supported by the well along the reaction path, which is manifested as metastable resonances on the probability curves. The MgD + products are obtained via a non-adiabatic pathway, and the reaction is more efficient than the quenching progress at the selected collision energies. The product angular distributions present obvious forward scattering bias, and the weak backward scatterings are mainly contributed by the new partial waves that are opened as the collision energy increases. Further rovibrational state-resolved results reflect that the predominant forward scattering correlates with the internally hot products and the backward-scattered products occupy the colder vibrational and rotational states.

Quantum calculations for the abstraction and exchange channels of the H + SH+(v0 = 0, j0 = 0) reaction

The dynamical calculations for the abstraction and exchange channels of the H + SH + ( v 0 = 0, j 0 = 0) reaction are carried out by using time-dependent wave packet method. Some dynamics properties are reported and compared with available theoretical studies. In general, good agreement is achieved between present values and Zanchet’s results in the collision energy range studied. The results of the differential cross section indicated that the forward biased abstraction mechanism dominates the reaction for the abstraction channel. While the “head-on” rebound mechanism plays a dominant role in the exchange channel.

A study on the non-adiabatic dynamics of the Li(2p) + H2 → Li(2 s) + H2 quenching reaction calculated by time-dependent wavepacket method

A non-adiabatic time-dependent wave packet calculations of the quenching reaction Li(2p) + H2 → Li(2 s) + H2 are carried out based on a diabatic potential energy surface (PES). The integral cross sections (ICSs) and reaction probabilities are calculated at the state-to-state level. In addition, the ICSs and reaction probabilities of the abstraction reaction are compared with the quenching reaction. According to the ICSs with different vibrational state of H2, we argue that the potential well along the reaction path has an important influence on the non-adiabatic transition.

State-to-state Rate Constants for the H + LiH(v 0 = 0, j 0 = 0) Reaction: An Accurate Nonadiabatic Dynamical Study

Abstract The state-to-state rate constants for hydrogen abstraction, nonadiabatic hydrogen abstraction, and exchange channels of the H + LiH reaction have been studied in the temperature range from 10 to 5000 K by using the nonadiabatic time-dependent wave packet method. The total and vibrational state-resolved rate constants of the H + LiH (v 0 = 0, j 0 = 0) → Li(22S) + H2 reaction are calculated and compared with previous adiabatic values. The results indicated that adiabatic values always overestimate the rate constant due to the nonadiabatic effect not being considered. In addition, the ratio of adiabatic vibrational state-resolved rate constants versus that of nonadiabatic ones is calculated for the hydrogen abstraction channel. This reflects that the nonadiabatic effect is mainly focused on the low-lying vibrational states. Moreover, the rovibrational state-resolved rate constants show that the largest population of product is located at (v′ = 2, j′ = 11), (v′ = 0, j′ = 5), and (v′ = 0, j′ = 6) for the hydrogen abstraction, nonadiabatic hydrogen abstraction and exchange channels, respectively. The total and vibrational state-resolved rate constants of the Li(22P) → Li(22S) quenching process are also calculated in the temperature range up to 5000 K. The results show that when the temperature is lower than 200 K, the quenching efficiency increases rapidly, but with the further increase of temperature, the quenching efficiency hardly changes.

Accurate High-Level Ab Initio-Based Global Potential Energy Surface and Quantum Dynamics Calculation for the First Excited State of CH2.

A full three-dimensional global potential energy surface (PES), covering the whole configuration space, is reported first for the title system by fitting high-level ab initio energies at the multireference configuration interaction level with the aug-cc-pV6Z basis set. In this work, the many-body expansion method is invoked to fit the innate character of the CH2+(12A″) PES. The topographical features are examined in detail based on the new global PES and in accordance with the other calculations from the ab initio energies, which show the correct behavior at the C+(2P) + H2(X1Σg+) and CH+(a3Π) + H(2S) dissociation limits. Using a time-dependent wave packet method, we provide insights into the dynamics behavior for reaction of C+(2P) + H2(X1Σg+) → CH+(a3Π) + H(2S). The integral cross sections and reaction probabilities increase monotonically in terms of the collision energy.

Control of photodissociation of the molecular ion HD+ with two completely overlapping laser pulses

The dissociation dynamics of molecular ion HD+ in two completely overlapping THz and infrared pulses are investigated by using the time-dependent quantum wave packet method. The angular distribution of fragments depends on the carrier-envelope phase (CEP) of the THz pulse. The infrared pulse is employed to control the dissociation probability and the direction of the products D+H+. When the intensity of infrared pulse is 2.0×1014 W/cm2, the molecule HD+ is pre-oriented by the THz pulse and most of products D+H+ and H+D+ are distributed in the same direction. When the intensity is increased to 4.6×1014 W/cm2, the angular distribution is mainly generated by the THz pulse after molecular ions are dissociated, and the direction of products D+H+ is opposite to that of products H+D+.

Theoretical investigation of pump–probe photoelectron spectroscopy on KLi

Based on the time-dependent quantum wave packet method, the ionization dynamics of the KLi molecule are theoretically simulated using the pump–probe technique. The Autler–Townes splitting phenomenon of photoelectron spectroscopy is analyzed by changing the laser pulse width, the intensity of the probe laser pulse, and the delay time between the pump and probe pulses. It has been found that the height difference between the splitting peaks becomes larger as the width of the pump pulse increases under the resonant condition. Furthermore, the probe laser with large pulse width has little effect on the peak height difference compared with the pump pulse, but it results in multi-splitting of the photoelectron spectroscopy. Meanwhile, the effect of delay time on the splitting peaks in photoelectron spectroscopy is investigated.

Theoretical Study of the Energy Disposal Mechanism and the State-Resolved Quantum Dynamics of the H + LiH+ → H2 + Li+ Reaction.

Despite several studies in the literature, the detailed quantum state-to-state level mechanism of the astrophysically important exoergic barrierless H + LiH+ → H2 + Li+ reaction is yet to be understood. In this work, we have investigated the energy disposal mechanism of the reaction in terms of integral reaction cross section, product internal state distributions, differential cross section, and rate constant. Fully converged and Coriolis coupled quantum mechanical calculations based on a time-dependent wave packet method have been performed at the state-to-state level on the ab initio electronic ground state potential energy surface (PES) constructed by Martinazzo et al. (J. Chem. Phys. 2003, 119, 11241-11248). The agreement between the present quantum mechanical and previous quasi-classical results is found even at very low relative translational energies of reagents. A non-statistical inverse Boltzmann vibrational distribution for the product is found. This is attributed to the "attractive" nature of the underlying PES, which facilitates the excess energy release mostly as product vibration (60-80%). The energy disposal in products is found to be unaffected by the rovibrational excitation of the reagent diatom due to the weak coupling between the vibrational modes of the reagent and the product. The mild effect of collision energy on the product energy disposal is ascribed to the effective coupling between the translational modes of the reagent and the product. It is found that the collisions lead to the formation of the product H2 in its rovibrationally excited levels.

A new global potential energy surface of X2A′ state of Li2H system and quantum dynamics calculation of the H + Li2 → Li + LiH reaction

A new potential energy surface (PES) of the ground state (X 2 A′) of Li 2 H was built using 18,403 ab initio points. The MRCI-F12 method with AVQZ basis set were used in the ab initio calculation. Furthermore, the widely used permutation invariant polynomial neural network method was adopted in the fitting process. The features of new PES were compared with previous theoretical and experimental studies. The results indicated that the spectroscopic parameters of PES are in good agreement with experimental data. In addition, the dynamics calculations of the H + Li 2 → Li + LiH reaction were carried out using time-dependent wave packet method based on the new PES. The dynamics properties such as reaction probability, integral cross section and thermal rate constant were reported and compared with previous theoretical studies.