76 research outputs found
Controllable binding of polar molecules and meta-stability of 1-D gases with attractive dipole forces
We explore one-dimensional (1-D) samples of ultracold polar molecules with
attractive dipole-dipole interactions and show the existence of a repulsive
barrier due to a strong quadrupole interaction between molecules. This barrier
can stabilize a gas of ultracold KRb molecules and even lead to long-range
wells supporting bound states between molecules. The properties of these wells
can be controlled by external electric fields, allowing the formation of long
polymer-like chains of KRb, and studies of quantum phase transitions by varying
the effective interaction between molecules. We discuss the generalization of
those results to other systems
Approximating electronically excited states with equation-of-motion linear coupled-cluster theory
A new perturbative approach to canonical equation-of-motion coupled-cluster
theory is presented using coupled-cluster perturbation theory. A second-order
M{\o}ller-Plesset partitioning of the Hamiltonian is used to obtain the well
known equation-of-motion many-body perturbation theory (EOM-MBPT(2)) equations
and two new equation-of-motion methods based on the linear coupled-cluster
doubles (EOM-LCCD) and linear coupled-cluster singles and doubles (EOM-LCCSD)
wavefunctions. This is achieved by performing a short-circuiting procedure on
the MBPT(2) similarity transformed Hamiltonian. These new methods are
benchmarked against very accurate theoretical and experimental spectra from 25
small organic molecules. It is found that the proposed methods have excellent
agreement with canonical EOM-CCSD state for state orderings and relative
excited state energies as well as acceptable quantitative agreement for
absolute excitation energies compared with the best estimate theory and
experimental spectra.Comment: 9 pages 3 figure
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