166 research outputs found
Long range intermolecular forces in triatomic systems: connecting the atom-diatom and atom-atom-atom representations
The long-range forces that act between three atoms are analysed in both
atom-diatom and atom-atom-atom representations. Expressions for atom-diatom
dispersion coefficients are obtained in terms of 3-body nonadditive
coefficients. The anisotropy of atom-diatom C_6 dispersion coefficients arises
primarily from nonadditive triple-dipole and quadruple-dipole forces, while
pairwise-additive forces and nonadditive triple-dipole and
dipole-dipole-quadrupole forces contribute significantly to atom-diatom C_8
coefficients. The resulting expressions are applied to dispersion coefficients
for Li + Li_2 (triplet) and recommendations are made for the best way to obtain
global triatomic potentials that dissociate correctly both to three separated
atoms and to an atom and a diatomic molecule.Comment: To be published in a special issue of Molecular Physics in honour of
Mark Chil
Ab initio investigation of intermolecular interactions in solid benzene
A computational strategy for the evaluation of the crystal lattice constants
and cohesive energy of the weakly bound molecular solids is proposed. The
strategy is based on the high level ab initio coupled-cluster determination of
the pairwise additive contribution to the interaction energy. The
zero-point-energy correction and non-additive contributions to the interaction
energy are treated using density functional methods. The experimental crystal
lattice constants of the solid benzene are reproduced, and the value of 480
meV/molecule is calculated for its cohesive energy
Near-dissociation states and coupled potential curves for the HeN+ complex
The near-dissociation microwave rovibronic spectra of HeN+ [Carrington et al., Chem. Phys. Lett. 262, 598 (1996)] are used to obtain coupled potential energy curves for the six electronic states correlating with He+N+ 3P0, 3P1, and 3P2. High-quality ab initio calculations are carried out, using a spin-restricted open-shell coupled-cluster method with an augmented correlation-consistent quintuple-zeta basis set (aug-cc-pV5Z). Fully coupled calculations of bound and quasibound states are performed, including all six electronic states, and suggest two possible assignments of the observed transitions. The potentials are then morphed (scaled) to reproduce the experimental frequencies. One of the two assignments, designated SH1, is preferred because it gives a more satisfactory explanation of the observed hyperfine splittings. The corresponding morphed potential has well depths of 1954 cm−1 and 192 cm−1 for the spin-free 3Σ− and 3Π curves, respectively
On the long-range and short-range behavior of potentials from reproducing kernel Hilbert space interpolation
Cold collisions of OH and Rb. I: the free collision
We have calculated elastic and state-resolved inelastic cross sections for
cold and ultracold collisions in the Rb() + OH() system,
including fine-structure and hyperfine effects. We have developed a new set of
five potential energy surfaces for Rb-OH() from high-level {\em ab
initio} electronic structure calculations, which exhibit conical intersections
between covalent and ion-pair states. The surfaces are transformed to a
quasidiabatic representation. The collision problem is expanded in a set of
channels suitable for handling the system in the presence of electric and/or
magnetic fields, although we consider the zero-field limit in this work.
Because of the large number of scattering channels involved, we propose and
make use of suitable approximations. To account for the hyperfine structure of
both collision partners in the short-range region we develop a
frame-transformation procedure which includes most of the hyperfine
Hamiltonian. Scattering cross sections on the order of cm are
predicted for temperatures typical of Stark decelerators. We also conclude that
spin orientation of the partners is completely disrupted during the collision.
Implications for both sympathetic cooling of OH molecules in an environment of
ultracold Rb atoms and experimental observability of the collisions are
discussed.Comment: 20 pages, 16 figure
Three-body non-additive forces between spin-polarized alkali atoms
Three-body non-additive forces in systems of three spin-polarized alkali
atoms (Li, Na, K, Rb and Cs) are investigated using high-level ab initio
calculations. The non-additive forces are found to be large, especially near
the equilateral equilibrium geometries. For Li, they increase the three-atom
potential well depth by a factor of 4 and reduce the equilibrium interatomic
distance by 0.9 A. The non-additive forces originate principally from chemical
bonding arising from sp mixing effects.Comment: 4 pages, 3 figures (in 5 files
Acceptance and uptake of improved biomass cookstoves in Peru: learning from system level approaches to transform large-scale cooking interventions
Improved biomass cookstoves (ICS) are cooking technologies that increase wellbeing and reduce household air pollution. With the goal of identifying factors influencing ICS acceptance and uptake at five system levels (intrapersonal, interpersonal, community, institutional, and policy), we carried out a qualitative study in three regions in Peru. We conducted 32 focus group discussions (243 ICS users) and 26 semi-structured interviews with key stakeholders, applying a combination of two system-level frameworks for analysis: the socio-ecological model and the ICS adoption domain. Enabling and impeding factors at each level were closely related to each other. Decisions made by policy makers - often centralised and not considering local/regional realities - strongly influenced acceptance and barriers at lower levels. ICS acceptance and uptake tended to be low when ICS users were not involved from the start. Most ICS programmes focused on stove distribution outputs, without considering community needs, such as training on ICS building, maintenance and repair, or issues related to spare part availability, which is a strong barrier to sustained uptake of ICS. Using a combination of models that allows one to examine facilitators and barriers at multiple levels, as well as the interactions of those levels, was useful in assessing potential improvements to intervention design, facilitating programme success, preventing unforeseen programme adaptations, and improving cost-effectiveness of interventions
Contribución del Flipped classroom en aprendizaje significativo de la biología celular durante la educación médica
Con la presente investigación se determinó la contribución del Flipped classroom en el aprendizaje de la biología
celular con razonamiento crítico. Una estrategia activa que promueve el desarrollo de nuevas competencias
profesionales y cambios de paradigmas del docente en su práctica pedagógica. El abordaje investigativo realizado
ha sido cuasi experimental con enfoque cuantitativo y analítico en 54 estudiantes sometidos a 08 sesiones
virtuales como presenciales integrando el modelo Flipped classroom y a una prueba objetiva de 20 ítems, como
instrumento de recolección de datos. Instrumento validado por cinco especialistas del área y un grupo piloto de
estudiantes, alcanzando un coeficiente de confiabilidad alfa de Cronbach de 0,678. Los resultados obtenidos
luego de aplicar esta estrategia didáctica, revela una disminución del 68% al 28% de estudiantes en nivel no
logrado; un incremento del 32% al 64% en un nivel en proceso, y desde un 0% al 8%. en un nivel destacado.
Hallazgos que luego de ser estimados con los estadísticos de pruebas descriptiva con p ˂ 0,05; y de pruebas
inferenciales como la prueba de Wilcoxon y Mann Whitney con significancia estadística (p=0,003) y confiabilidad
de 0,678), en muestras relacionadas en muestras y no relacionadas respectivamente, fundamenta que incorporar
Flipped classroom o “clase invertida” fortalece las dimensiones del aprendizaje: conocer, comprender, aplicar y
analizar, de las asignaturas de ciencias básicas, que generan rechazo en el estudiante de medicina que ingresan a
la universidad
Density Functional Theory Approach to Noncovalent Interactions via Interacting Monomer Densities
A recently proposed "DFT+dispersion" treatment (Rajchel et al., Phys. Rev.
Lett., 2010, 104, 163001) is described in detail and illustrated by more
examples. The formalism derives the dispersion-free density functional theory
(DFT) interaction energy and combines it with the dispersion energy from
separate DFT calculations. It consists in the self-consistent polarization of
DFT monomers restrained by the exclusion principle via the Pauli blockade
technique. Within the monomers a complete exchange-correlation potential should
be used, but between them only the exact exchange operates. The applications to
wide range of molecular complexes from rare-gas dimers to H-bonds to
pi-electron interactions show good agreement with benchmark values.Comment: 9 pages, 5 figures, 2 tables, REVTeX
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