Search

A semi-classical transport model, namely, quantum molecular dynamics (QMD) model, is employed for the theoretical study of nuclear dynamics in case of 197Au+197Au collisions at different beam energies from 20 to 1000 MeV/nucleon and at impact parameters from b = 0 to 13 fm using soft equation of state (EOS). In particular, we study the energy and impact parameter dependence of various quantities like average and maximum density, collision rate and participant-spectator matter. Our findings clearly indicate a significant energy and impact parameter dependence of all quantities. Interestingly, we observed that the variation of the impact parameter leads to drastic change in the participant/spectator matter up to 400 MeV/nucleon, whereas beyond 400 MeV/nucleon, nearly impact parameter independent results are found.

In this paper, the ultrafast dissociation following Cl 2p core–shell excitation into the 10a1* antibonding orbital in CH2Cl2 and CD2Cl2 molecules is studied. It is observed the presence of atomic Auger lines associated to the decay of dissociated Cl* atoms. The choice of CH2Cl2 and CD2Cl2 molecules to study the competition between the atomic and molecular Auger decays, allow us to probe nuclear dynamics and electron relaxation occurring on a comparable time scale, keeping other parameters identical.In this paper, the ultrafast dissociation following Cl 2p core–shell excitation into the 10a1* antibonding orbital in CH2Cl2 and CD2Cl2 molecules is studied. It is observed the presence of atomic Auger lines associated to the decay of dissociated Cl* atoms. The choice of CH2Cl2 and CD2Cl2 molecules to study the competition between the atomic and molecular Auger decays, allow us to probe nuclear dynamics and electron relaxation occurring on a comparable time scale, keeping other parameters identical.

We propose a "backtracking" mechanism within Tully's fewest switches surface hopping (FSSH) algorithm, whereby whenever one detects consecutive (double) hops during a short period of time, one simply rewinds the dynamics backward in time. In doing so, one reduces the number of hopping events and comes closer to a truly fewest switches surface hopping approach with independent trajectories. With this algorithmic change, we demonstrate that surface hopping can be reasonably accurate for nuclear dynamics in a multidimensional configuration space with a complex-valued (i.e., not real-valued) electronic Hamiltonian; without this adjustment, surface hopping often fails. The added computational cost is marginal. Future research will be needed to assess whether or not this backtracking correction can improve the accuracy of a typical FSSH calculation with a real-valued electronic Hamiltonian (that ignores spin).

We present a 3D quantum wavepacket method for calculating state-to-state reactive cross sections for the A+BC→AC+B reaction. The method avoids the coordinate problem (of A+BC arrangements being difficult to represent by AC+B coordinates, and vice versa) by solving the reactant-product decoupling (RPD) equations [T. Peng and J. Z. H. Zhang, J. Chem. Phys. 105, 6072 (1996)] in their further partitioned form [S. C. Althorpe, D. J. Kouri, and D. K. Hoffman, J. Chem. Phys. 107, 7816 (1997)]. These equations decouple the nuclear dynamics Schrodinger equation into separate reactant, strong-interaction, and product regions, permitting different coordinates to be used in each region. We solve the equations using A+BC Jacobi coordinates in the reactant region, and AC+B Jacobi coordinates in the strong-interaction and product regions. In test calculations on the J=0 H+H2 reaction, we show that this partitioning of coordinate systems is much more efficient than using A+BC coordinates in the strong-interaction region ...

Coherent states suitable for the description of molecular rotations are developed and their connection to similar coherent states in the literature are explored. In particular their quasiclassical properties are developed. The use of such coherent states in time-dependent electron nuclear dynamics studies of molecular collision processes is discussed.

The reactive collisions of protons with methane molecules at 30 eV in the laboratory frame are studied with the electron nuclear dynamics (END). The results from this theoretical approach, which does not invoke the Born–Oppenheimer approximation and does not impose any constraints on the nuclear dynamics, are compared to the results from time-of-flight measurements. Total differential cross sections and integral cross sections as well as fragmentation ratios and energy loss spectra are discussed.

The free dianionic Si2O2−5 system is studied by standard ab initio methods. We have located three distinct isomers in the Si2O2−5 system. All three Si2O2−5 isomers are found to be thermodynamically stable with respect to dissociation into monoanionic fragments. However, only two of them are predicted to be clearly stable with respect to vertical electron autodetachment. Minimal energy pathways which interconnect the three isomers have been studied together with the binding energy of the excess electron along them. The results give rise to an unusual nuclear dynamics problem. In particular, the associated barriers have been found to be high and wide enough to predict long lifetimes for two free dianionic species.

Proton collisions with hydrogen molecules at 30 eV in the laboratory frame is a simple ion‐molecule system exhibiting a number of distinct processes such as inelastic scattering, charge transfer, rearrangement, and dissociation. The electron nuclear dynamics (END) theory which allows full electron nuclear coupling and which does not restrict the system from reaching any of the possible product channels, is applied to this sytem to produce transition probabilities, differential, and integral (vibrationally resolved) cross sections. Comparisons with experiment demonstrate that END, even in its simplest implementation, with a single determinantal state for the electrons and with classical nuclei, yields results that are competitive with other theoretical approaches.

This is a reply to the comment by J. L. Alonso et al. (arXiv:1302.6146; to appear in J. Chem. Phys) on our paper A. Abedi, N. T. Maitra, and E. K. U. Gross, J. Chem. Phys. 137, 22A530 (2012) [arXiv: 1208.4388]

The astrophysically relevant system H(+) + CO (v(i) = 0) → H(+) + CO (v(f)) at E(Lab) = 30 eV is studied with the simplest-level electron nuclear dynamics (SLEND) method. This investigation follows previous successful SLEND studies of H(+) + H(2) and H(+) + N(2) at E(Lab) = 30 eV [J. Morales, A. Diz, E. Deumens, and Y. Öhrn, J. Chem. Phys. 103(23), 9968 (1995); C. Stopera, B. Maiti, T. V. Grimes, P. M. McLaurin, and J. A. Morales, J. Chem. Phys. 134(22), 224308 (2011)]. SLEND is a direct, time-dependent, variational, and non-adiabatic method that adopts a classical-mechanics description for the nuclei and a single-determinantal wavefunction for the electrons. A canonical coherent-states (CS) procedure associated with SLEND reconstructs quantum vibrational properties from the SLEND classical dynamics. Present SLEND results include reactivity predictions, snapshots of the electron density evolution, average vibrational energy transfers, rainbow angle predictions, total and vibrationally resolved differential cross sections (DCS), and average vibrational excitation probabilities. SLEND results are compared with available data from experiments and vibrational close-coupling rotational infinite-order sudden (VCC-RIOS) approximation calculations. Present simulations employ four basis sets: STO-3G, 6-31G, 6-31G**, and cc-pVDZ to determine their effect on the results. SLEND simulations predict non-charge-transfer scattering and CO collision-induced dissociation as the main reactions. SLEND/6-31G, /6-31G**, and /cc-pVDZ predict rainbow angles and total DCS in excellent agreement with experiments and more accurate than their VCC-RIOS counterparts. SLEND/6-31G** and /cc-pVDZ predict vibrationally resolved DCS for v(f) = 0-2 in satisfactory experimental agreement, but less accurate than their comparable H(+) + CO VCC-RIOS and H(+) + H(2) and H(+) + N(2) SLEND results. SLEND∕6-31G** and ∕cc-pVDZ predict qualitatively correct average vibrational excitation probabilities, which are quantitatively correct for v(f) = 2, but under(over)estimated for v(f) = 0(1). Discrepancies in some H(+) + CO SLEND vibrational properties, not observed in H(+) + H(2) and H(+) + N(2) SLEND results, are attributed to the moderately overestimated SLEND vibrational energy through its effect upon the canonical CS probabilities. Correction of that energy to its experimental values produces a remarkable improvement in the average vibrational excitation probabilities. Ways to obtain more accurate vibrational properties with higher-level versions of electron nuclear dynamics are discussed.

We report wavepacket dynamics on a model system with a three-state conical intersection. Quantum wavepacket dynamics using the multiconfigurational time-dependent Hartree method have been carried out for the T ⊗ (e + t(2)) Jahn-Teller problem, using a Jahn-Teller vibronic model Hamiltonian. The effects of the magnitude of the coupling parameters and of the initial position of the wavepacket on the dynamics around the three-state conical intersection have been considered. It was found that the effect of the coupling strength is not dramatic for the population transfer in most cases, but the details of the dynamics and the involvement of the different modes are affected by it.

In this paper, we construct a phase-space surface hopping algorithm for use in systems that exhibit strong nonadiabatic coupling. The algorithm is derived from a representation of the electronic basis which is a function of the nuclear phase-space coordinates rather than the nuclear position coordinates. This phase-space adiabatic basis can be understood in the context of Berry's superadiabatic basis formalism as the first-order superadiabatic correction to the conventional position-space adiabatic basis. This superadiabatic representation leads to nuclear dynamics described not by Newton's equations of motion but by generalized Hamilton's equations of motion. The phase-space surface hopping algorithm captures physical effects that cannot be described by traditional algorithms. For a simple model problem, we show that phase-space surface hopping is more accurate than position-space surface hopping, especially when the nonadiabatic coupling is strong.

The existence of a seam of conical intersection, the reference seam, does not rule out the existence of additional disjoint seams of conical intersection. These disjoint seams intersect the g-h planes of the reference seam, a region usually assumed to be devoid of intersections, potentially leading to unexpected points of degeneracy in close proximity to the original conical intersection. Here the authors show how the locus of these disjoint seams can be predicted employing a Hamiltonian derived from second-order perturbation theory. Dramatic differences between the g-h planes of the reference and disjoint seams are found and are expected to have a profound impact on nuclear dynamics. Numerical studies of both high symmetry (D(3h), C(3)H(3)) and low symmetry (C(2v), C(2)H(2)N) species are presented.

The CO and CO(2) carbon and oxygen Auger spectra have been measured by electron impact and compared with accurate theoretical calculations accounting for the effects of the dynamics of the nuclei on the energy and linewidth of the Auger bands. The calculations for CO were previously published [L. S. Cederbaum et al., J. Chem. Phys. 95, 6634 (1991)], while for CO(2) they are new and presented here for the first time. For both molecules, particular attention has been paid to the low-kinetic-energy region of the spectra, which corresponds to doubly charged ion states with the two holes mainly localized in the inner valence region. New bands have been observed. It is shown that a proper consideration of the vibrational broadening and shift of the bands due to the dynamics of the nuclei is needed to assign these features. For CO, very large energy shifts between corresponding features in the C 1s and O 1s spectra have been observed, confirming the theoretical predictions of 1991. The new computed spectra of CO(2) allow a very accurate analysis of the experiments over the whole energy range.

The conceptual description of nuclear dynamics near a conical intersection generally focuses on the branching plane, the two-dimensional subspace in which the conical topography is evinced, to the exclusion of the seam coordinates, the remaining internal nuclear coordinates. Establishing the limits of the utility of this assumption is an important issue in nonadiabatic dynamics. To accomplish this a careful treatment of the nuclear dynamics near conical intersections is required. The coordinate systems generally available for describing conical intersections are not optimal for such studies. In this work we extend a perturbative description of a conical intersection to describe more general seam spaces. We develop a coordinate system that segregates the interactions coupling the branching plane to the seam space into a set of gateway modes. The size of this set does not increase with the size of the molecule. The gateway modes are illustrated for the 1,2 1A conical intersections in NH3. The connection between the gateway modes and the optimum coordinate system for locating and characterizing seam confluences, intersections of two branches of the same seam, is discussed.

In recent years, a new field of nuclear research has been opened through the possibility of studying nuclei with very large values of the angular momentum. This development has been closely associated with the study of heavy‐ion reactions, since collisions between two heavy nuclei are especially effective in producing metastable compound systems with large angular momenta. The study of such rapidly rotating nuclear systems provides the opportunity for exploring new aspects of nuclear dynamics. In figure 1 we show a multiple‐coincidence spectrometer for studying gamma‐ray cascades from the decay of these high‐angular‐momentum states. It comprises eighteen NaI detectors arranged around an on‐line target; seven of the detectors and their photo‐multipliers are visible in the photo. The arrangement gives high sensitivity to gamma‐ray cascades, which in some cases exceed thirty consecutive gamma rays. The spectrometer was constructed at the Niels Bohr Institute and is being used in a Copenhagen‐Darmstadt collab...

We consider a linear antiferromagnetic chain of elastically coupled spins in the Hartree‐Fock approximation to the Heisenberg Hamiltonian. The nuclear dynamics is neglected. The instability of the system is investigated and the results are compared with the X‐Y model treated in I. It is shown that the Hartree‐Fock approximation is essentially equivalent to a renormalization of the exchange integral in the X‐Y model.