1,003 research outputs found
Linear response functions for a vibrational configuration interaction state
Linear response functions are implemented for a vibrational configuration interaction state allowing accurate analytical calculations of pure vibrational contributions to dynamical polarizabilities. Sample calculations are presented for the pure vibrational contributions to the polarizabilities of water and formaldehyde. We discuss the convergence of the results with respect to various details of the vibrational wave function description as well as the potential and property surfaces. We also analyze the frequency dependence of the linear response function and the effect of accounting phenomenologically for the finite lifetime of the excited vibrational states. Finally, we compare the analytical response approach to a sum-over-states approac
Non-covalent interactions across organic and biological subsets of chemical space: Physics-based potentials parametrized from machine learning
Classical intermolecular potentials typically require an extensive
parametrization procedure for any new compound considered. To do away with
prior parametrization, we propose a combination of physics-based potentials
with machine learning (ML), coined IPML, which is transferable across small
neutral organic and biologically-relevant molecules. ML models provide
on-the-fly predictions for environment-dependent local atomic properties:
electrostatic multipole coefficients (significant error reduction compared to
previously reported), the population and decay rate of valence atomic
densities, and polarizabilities across conformations and chemical compositions
of H, C, N, and O atoms. These parameters enable accurate calculations of
intermolecular contributions---electrostatics, charge penetration, repulsion,
induction/polarization, and many-body dispersion. Unlike other potentials, this
model is transferable in its ability to handle new molecules and conformations
without explicit prior parametrization: All local atomic properties are
predicted from ML, leaving only eight global parameters---optimized once and
for all across compounds. We validate IPML on various gas-phase dimers at and
away from equilibrium separation, where we obtain mean absolute errors between
0.4 and 0.7 kcal/mol for several chemically and conformationally diverse
datasets representative of non-covalent interactions in biologically-relevant
molecules. We further focus on hydrogen-bonded complexes---essential but
challenging due to their directional nature---where datasets of DNA base pairs
and amino acids yield an extremely encouraging 1.4 kcal/mol error. Finally, and
as a first look, we consider IPML in denser systems: water clusters,
supramolecular host-guest complexes, and the benzene crystal.Comment: 15 pages, 9 figure
Can realistic nuclear interactions tolerate a resonant tetraneutron ?
The possible existence of four-neutron resonances close to the physical
energy region is explored. Faddeev-Yakubovsky equations have been solved in
configuration space using realistic nucleon-nucleon interaction models. Complex
Scaling and Analytical Continuation in the Coupling Constant methods were used
to follow the resonance pole trajectories, which emerge out of artificially
bound tetraneutron states. The final pole positions for four-neutron states lie
in the third energy quadrant with negative real energy parts and should thus
not be physically observable.Comment: 10 pages, 6 figs, 2 tables. To be published in Phys. Rev.
Charge transport through single molecules, quantum dots, and quantum wires
We review recent progresses in the theoretical description of correlation and
quantum fluctuation phenomena in charge transport through single molecules,
quantum dots, and quantum wires. A variety of physical phenomena is addressed,
relating to co-tunneling, pair-tunneling, adiabatic quantum pumping, charge and
spin fluctuations, and inhomogeneous Luttinger liquids. We review theoretical
many-body methods to treat correlation effects, quantum fluctuations,
nonequilibrium physics, and the time evolution into the stationary state of
complex nanoelectronic systems.Comment: 48 pages, 14 figures, Topical Review for Nanotechnolog
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