1,587 research outputs found
Crystal structure and electronic states of tripotassium picene
The crystal structure of potassium doped picene with an exact stoichiometry
(K3C22H14, K3picene from here onwards) has been theoretically determined within
Density Functional Theory allowing complete variational freedom of the crystal
structure parameters and the molecular atomic positions. A modified herringbone
lattice is obtained in which potassium atoms are intercalated between two
paired picene molecules displaying the two possible orientations in the
crystal.Along the c-axis, organic molecules alternate with chains formed by
three potassium atoms. The electronic structureof the doped material resembles
pristine picene, except that now the bottom of the conduction band is occupied
by six electrons coming from the ionized K atoms (six per unit cell).
Wavefunctions remain based mainly on picene molecular orbitals getting their
dispersion from intralayer edge to face CH/pi bonding, while eigenenergies have
been modified by the change in the electrostatic potential. The small
dispersion along the c-axis is assigned to small H-H overlap. From the
calculated electronic density of states we expect metallic behavior for
potassium doped picene.Comment: Published version: 8 twocolumn pages, 7 color figures, 2 structural
.cif files include
The role of potassium orbitals in the metallic behavior of K3picene
Detailed electronic structure calculations of picene clusters doped by
potassium modeling the crystalline K3picene structure show that while two
electrons are completely transferred from potassium atoms to the LUMO of
pristine picene, the third one remains closely attached to both material
components. Multiconfigurational analysis is necessary to show that many
structures of almost degenerate total energies compete to define the cluster
ground state. Our results prove that the 4s orbital of potassium should be
included in any interaction model describing the material. We propose a quarter
filled two orbital model as the most simple model capable of describing the
electronic structure of K-intercalated picene. Precise solutions obtained by a
development of Lanczos method show low energy electronic excitations involving
orbitals located at different positions. Consequently, metallic transport is
possible in spite of the clear dominance of interaction over hopping.Comment: 12 pages, 10 figures (6 of them really heavy
Ciclo diario de la precipitación en las Islas Baleares
Se han recopilado los datos de precipitación horaria de 9 estaciones meteorológicas automáticas de las
Islas Baleares que abarcan entre 14 y 19 años de observación. Con esta información se ha estudiado cómo varía el
ciclo diario de la precipitación a lo largo del año, encontrando una gran regularidad en noviembre y diciembre, que
luego da paso a un aumento de las precipitaciones durante la madrugada y, sobre todo en la mitad cálida del año, en
las horas centrales del día. En conjunto, el mínimo de precipitación tiene lugar hacia el final de la tarde
Primeras medidas de irradiación solar en Palma de Mallorca.
Abstract not availabl
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