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

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

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

Aplicación de una recta de Teissier a la depuración de una base de datos termopluviométricos mensuales

Se han ensayado varios métodos, basados en el análisis de regresión, para rellenar y depurar series termopluviométricas mensuales y anuales. La regresión simple (modelo I) ha proporcionado resultados similares a los de la recta de Teissier en las series termométricas, si bien en las pluviométricas esta última ha mejorado ligeramente la calidad de las estimaciones. En cambio, en el caso de las precipitaciones anuales, tanto una como otra han resultado inadecuadas, especialmente en casos de extrapolación, y se ha tenido que recurrir al sencillo método de las proporciones

Quimisme de 17 pluges de fang al terme municipal de Palma (Mallorca)

Es dóna a conèixer la química de 17 pluges de fang recol·lectades i analitzades, del terme municipal de Palma, durant el període comprès entre el gener de 1988 fins juny de 1990 ambdós inclosos. Tots els paràmetres estudiats queden alterats, respecte a la pluja normal, essent els increments més notables els de l’alcalinitat, calci i sulfats, seguits dels de la conductivitat, magnesi, sodi, potassi i clorurs.The chemistry of 17 analyzed dusty rain samples gathered at the Palma municipality from January 1988 to june 1990 is presented. All studied parameters show anomalous values when compared to the normal rainfall. Most noteworthy are increases in alkalinity, Calcium and Sulfates, followed by those of conductivity, Magnesium, Sodium, Potassium and Chlorides