1,030 research outputs found
Quantum dynamics in macrosystems with several coupled electronic states: hierarchy of effective Hamiltonians
We address the nonadiabatic quantum dynamics of macrosystems with several
coupled electronic states, taking into account the possibility of multi-state
conical intersections. The general situation of an arbitrary number of states
and arbitrary number of nuclear degrees of freedom (modes) is considered. The
macrosystem is decomposed into a system part carrying a few, strongly coupled
modes, and an environment, comprising the vast number of remaining modes. By
successively transforming the modes of the environment, a hierarchy of
effective Hamiltonians for the environment is constructed. Each effective
Hamiltonian depends on a reduced number of effective modes, which carry
cumulative effects. By considering the system's Hamiltonian along with a few
members of the hierarchy, it is shown mathematically by a moment analysis that
the quantum dynamics of the entire macrosystem can be numerically exactly
computed on a given time-scale. The time scale wanted defines the number of
effective Hamiltonians to be included. The contribution of the environment to
the quantum dynamics of the macrosystem translates into a sequential coupling
of effective modes. The wavefunction of the macrosystem is known in the full
space of modes, allowing for the evaluation of observables such as the
time-dependent individual excitation along modes of interest, as well a spectra
and electronic-population dynamics
Ab initio calculations with a nonspherical Gaussian basis set: Excited states of the hydrogen molecule
A basis set of generalized nonspherical Gaussian functions (GGTOs) is
presented and discussed. As a first example we report on Born-Oppenheimer
energies of the hydrogen molecule. Although accurate results have been
obtained, we conclude that H_2 is too 'simple' to allow for a substantial gain
by using nonspherical functions. We rather expect that these functions may be
particularly useful in calculations on large systems. A single basis set of
GGTOs was used to simultaneously calculate the potential energy curves of
several states within each subspace of {1,3}\Sigma_{g,u} symmetry. We hereby
considerd the entire region of internuclear distances 0.8 < R < 1000 a.u. In
particular the results for the fourth up to sixth electronic states show a high
accuracy compared to calculations which invoke explicitely correlated
functions, e.g. the relative accuracy is at least of the order of magnitude of
10^{-5}a.u. Energies for the 4 ^1\Sigma_u^+ and 4-6 ^3\Sigma_u^+ were improved
and accurate data for the 6 ^3\Sigma_g^+, 5 ^1\Sigma_u^+, and 6 ^1\Sigma_u^+
state are, to the best of the authors knowledge, presented for the first time.
Energy data for the seventh up to the nineth electronic state within each
subspace were obtained with an estimated error of the order of magnitude of
10^{-4}a.u. The 7 ^1\Sigma_g^+ and the 6 ^1\Sigma_u^+ state were found to
exhibit a very broad deep outer well at large internuclear distances.Comment: 4 figures, subm.to J.Chem.Phy
Electron-correlation driven capture and release in double quantum dots
We recently predicted that the interatomic Coulombic electron capture (ICEC)
process, a long-range electron correlation driven capture process, is
achievable in gated double quantum dots (DQDs). In ICEC an incoming electron is
captured by one QD and the excess energy is used to remove an electron from the
neighboring QD. In this work we present systematic full three-dimensional
electron dynamics calculations in quasi-one dimensional model potentials that
allow for a detailed understanding of the connection between the DQD geometry
and the reaction probability for the ICEC process. We derive an effective
one-dimensional approach and show that its results compare very well with those
obtained using the full three-dimensional calculations. This approach
substantially reduces the computation times. The investigation of the
electronic structure for various DQD geometries for which the ICEC process can
take place clarify the origin of its remarkably high probability in the
presence of two-electron resonances
Controlled energy-selected electron capture and release in double quantum dots
Highly accurate quantum electron dynamics calculations demonstrate that
energy can be efficiently transferred between quantum dots. Specifically, in a
double quantum dot an incoming electron is captured by one dot and the excess
energy is transferred to the neighboring dot and used to remove an electron
from this dot. This process is due to long-range electron correlation and shown
to be operative at rather large distances between the dots. The efficiency of
the process is greatly enhanced by preparing the double quantum dot such that
the incoming electron is initially captured by a two-electron resonance state
of the system. In contrast to atoms and molecules in nature, double quantum
dots can be manipulated to achieve this enhancement. This mechanism leads to a
surprisingly narrow distribution of the energy of the electron removed in the
process which is explained by resonance theory. We argue that the process could
be exploited in practice.Comment: Lette
Bound states of negatively charged ions induced by a magnetic field
We analyse the bound states of negatively charged ions which were predicted
to exist because of the presence of a magnetic field by Avron et al. We confirm
that the number of such states is infinite in the approximation of an
infinitely heavy nucleus and provide insight into the underlying physical
picture by means of a combined adiabatic and perturbation theoretical approach.
We also calculate the corresponding binding energies which are qualitatively
different for the states with vanishing and non-vanishing angular momentum. An
outlook on the case of including center of mass effects is presented.Comment: 14 pages, 2 figure
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