241 research outputs found
Early stages of radiation damage in graphite and carbon nanostructures: A first-principles molecular dynamics study
Understanding radiation-induced defect formation in carbon materials is
crucial for nuclear technology and for the manufacturing of nanostructures with
desired properties. Using first principles molecular dynamics, we perform a
systematic study of the non-equilibrium processes of radiation damage in
graphite. Our study reveals a rich variety of defect structures (vacancies,
interstitials, intimate interstitial-vacancy pairs, and in-plane topological
defects) with formation energies of 5--15 eV. We clarify the mechanisms
underlying their creation and find unexpected preferences for particular
structures. Possibilities of controlled defect-assisted engineering of
nanostructures are analyzed. In particular, we conclude that the selective
creation of two distinct low-energy intimate Frenkel pair defects can be
achieved by using a 90--110 keV electron beam irradiation.Comment: 5 pages, 4 figure
Non-adiabatic quantum dynamics with fermionic subspace-expansion algorithms on quantum computers
We introduce a novel computational framework for excited-states molecular
quantum dynamics simulations driven by quantum computing-based
electronic-structure calculations. This framework leverages the fewest-switches
surface-hopping method for simulating the nuclear dynamics, and calculates the
required excited-state transition properties with different flavors of the
quantum subspace expansion and quantum equation-of-motion algorithms. We apply
our method to simulate the collision reaction between a hydrogen atom and a
hydrogen molecule. For this system, we critically compare the accuracy and
efficiency of different quantum subspace expansion and equation-of-motion
algorithms and show that only methods that can capture both weak and strong
electron correlation effects can properly describe the non-adiabatic effects
that tune the reactive event
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