12,243 research outputs found
Approaching exact hyperpolarizabilities via sum-over-states Monte Carlo configuration interaction
We propose using sum-over-states calculations with the compact wavefunctions
of Monte Carlo configuration interaction to approach accurate values for
higher-order dipole properties up to second hyperpolarizabilities in a
controlled way. We apply the approach to small systems that can generally be
compared with full configuration interaction (FCI) results. We consider
hydrogen fluoride with a 6-31g basis and then look at results, including
frequency dependent properties, in an aug-cc-pVDZ basis. We extend one
calculation beyond FCI by using an aug-cc-pVTZ basis. The properties of an
H molecule with multireference character are calculated in an aug-cc-pVDZ
basis. We then investigate this method on a strongly multireference system with
a larger FCI space by modelling the properties of carbon monoxide with a
stretched geometry. The behavior of the approach with increasing basis size is
considered by calculating results for the neon atom using aug-cc-pVDZ to
aug-cc-pVQZ. We finally test if the unusual change in polarizability between
the first two states of molecular oxygen can be reproduced by this method in a
6-31g basis.Comment: 11 pages, 14 figure
Characterizing a configuration interaction excited state using natural transition geminals
We introduce natural transition geminals as a means to qualitatively
understand a transition where double excitations are important. The first two
singlet states of the CH cation are used as an initial example. We
calculate these states with configuration interaction singles (CIS) and
state-averaged Monte Carlo configuration interaction (SA-MCCI). For each method
we compare the important natural transition geminals with the dominant natural
transition orbitals. We then compare SA-MCCI and full configuration interaction
(FCI) with regards to the natural transition geminals using the beryllium atom.
We compare using the natural transition geminals with analyzing the important
configurations in the CI expansion to give the dominant transition for the
beryllium atom and the carbon dimer. Finally we calculate the natural
transition geminals for two electronic excitations of formamide.Comment: 15 pages, 2 figures. Mol. Phys. (2013
Photoracemization and excited state relaxation through non-adiabatic pathways in chromium (III) oxalate ions
Calculations of Potential Energy Surfaces Using Monte Carlo Configuration Interaction
We apply the method of Monte Carlo configuration interaction (MCCI) to
calculate ground-state potential energy curves for a range of small molecules
and compare the results with full configuration interaction. We show that the
MCCI potential energy curve can be calculated to relatively good accuracy, as
quantified using the non-parallelity error, using only a very small fraction of
the FCI space. In most cases the potential curve is of better accuracy than its
constituent single-point energies. We finally test the MCCI program on systems
with basis sets beyond full configuration interaction: a lattice of fifty
hydrogen atoms and ethylene. The results for ethylene agree fairly well with
other computational work while for the lattice of fifty hydrogens we find that
the fraction of the full configuration interaction space we were able to
consider appears to be too small as, although some qualitative features are
reproduced, the potential curve is less accurate.Comment: 14 pages, 22 figure
Monte Carlo configuration interaction applied to multipole moments, ionisation energies and electron affinities
The method of Monte Carlo configuration interaction (MCCI) [1,2] is applied
to the calculation of multipole moments. We look at the ground and excited
state dipole moments in carbon monoxide. We then consider the dipole of NO, the
quadrupole of the nitrogen molecule and of BH. An octupole of methane is also
calculated. We consider experimental geometries and also stretched bonds. We
show that these non-variational quantities may be found to relatively good
accuracy when compared with FCI results, yet using only a small fraction of the
full configuration interaction space. MCCI results in the aug-cc-pVDZ basis are
seen to generally have reasonably good agreement with experiment. We also
investigate the performance of MCCI when applied to ionisation energies and
electron affinities of atoms in an aug-cc-pVQZ basis. We compare the MCCI
results with full configuration-interaction quantum Monte Carlo [3,4] and
`exact' non-relativistic results [3,4]. We show that MCCI could be a useful
alternative for the calculation of atomic ionisation energies however electron
affinities appear much more challenging for MCCI. Due to the small magnitude of
the electron affinities their percentage errors can be high, but with regards
to absolute errors MCCI performs similarly for ionisation energies and electron
affinities.Comment: 12 pages, 20 figure
Applying Monte Carlo configuration interaction to transition metal dimers: exploring the balance between static and dynamic correlation
We calculate potential curves for transition metal dimers using Monte Carlo
configuration interaction (MCCI). These results, and their associated
spectroscopic values, are compared with experimental and computational studies.
The multireference nature of the MCCI wavefunction is quantified and we
estimate the important orbitals. We initially consider the ground state of the
chromium dimer. Next we calculate potential curves for Sc where we
contrast the lowest triplet and quintet states. We look at the molybdenum dimer
where we compare non-relativistic results with the partial inclusion of
relativistic effects via effective core potentials, and report results for
scandium nickel.Comment: 9 pages and 8 figure
Trajectory module of the NASA Ames Research Center aircraft synthesis program ACSYNT
A program was developed to calculate trajectories for both military and commercial aircraft for use in the aircraft synthesis program, ACSYNT. The function of the trajectory module was to calculate the changes in the vehicle's flight conditions and weight, as fuel is consumed, during the flying of one or more missions. The trajectory calculations started with a takeoff, followed by up to 12 phases chosen from among the following: climb, cruise, acceleration, combat, loiter, descent, and paths. In addition, a balanced field length was computed. The emphasis was on relatively simple formulations and analytic expressions suitable for rapid computation since a prescribed trajectory had to be calculated many times in the process of converging an aircraft design, or finding an optimum configuration. The trajectory module consists of about 2500 cards and operational on a CDC 7600 computer
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