Properties of simple metals beyond the local density approximation of density functional theory

We calculated lattice parameters, binding energies, bulk moduli, and phase stabilities of some simple metals: Li, Be, Na, Mg, and Al. Our ab initio all-electron calculations were done within the framework of density functional theory using the Crystal-98 program. The accuracy of different functionals for exchange and correlation energies that go beyond the local density approximation (LDA) was tested. The recent metageneralized gradient approximation proposed from Perdew et al. (Phys Rev Lett 1999, 82, 2544) gives lattice parameters that are better than the LDA values but not always better than the results of generalized gradient approximation. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 200

On how mild oxidation affects the structure of carbons: Comparative analysis by different techniques

Abstract Understanding how the structure of carbonaceous materials changes upon oxidation at mild temperature as a function of the graphitic order is of great importance for the development of clean combustion technologies, such as carbon fuel cells. The micro- and nanostructures of a range of carbon materials at room temperature and upon mild oxidation at 300 °C have been analysed by means of mercury porosimetry, Nitrogen adsorption, X-Ray Diffraction, Raman spectroscopy and Electron Paramagnetic Resonance. The samples included carbons with increasing level of graphitic order: three chars derived from two bituminous coals and a lignite, a synthetic carbon and a graphitized coke. The experimental characterization allows to classify the materials according to different structural parameters, including porosity, surface area, degree of graphitization and paramagnetic activation of the carbonaceous surface. A correlation with the rank of the analysed materials is observed. For the graphitized coke, oxidation leads to more crystalline order and enhancement of the paramagnetic signal. A similar increase in the paramagnetic activity is observed for the Lignite char. On the other hand, for the higher rank, bituminous and synthetic chars, mild oxidation leads to a slight expansion of the amorphous carbon and loss of paramagnetic activity. The differences are rationalized in terms of formation of new carbon-oxygen complexes on the graphitized coke and on the Lignite char, and redistribution of already existing complexes for the higher-rank coals. This investigation complements previous X-ray photoelectron spectroscopy measurements

A Combined Periodic Density Functional and Incremental Wave-Function-Based Approach for the Dipersion-Accounting Time-Resolved Dynamics of 4He Nanodroplets on Surfaces: 4He/Graphene

Helium-mediated Synthesis, Soft-landing and Spectroscopy of Metal Nanoparticles on Surfaces,CSIC, Madrid, Spain, October 10-11, 2014A general strategy to calculate accurate He-surface interaction potentials is proposed [1]. It extends the dispersionless density functional (dlDF) approach by Pernal et al. [2] to adsorbatesurface interactions by including periodic boundary conditions [1b]. A scheme to parametrize the dispersion interaction is introducced by calculating two- and three-body dispersion terms at CCSD(T) level via the method of increments [3]. The performance of the composite approach is tested on the low-lying selective adsorption states of 4He/graphene [5]. Second, its capability to describe dispersionless correlation effects realistically is used to extract dispersion effects in time-dependent density functional simulations on the collision of 4He droplets with graphene [1b]. Dispersion effects play a key role in the fast spreading of the 4He nanodroplet [1b,6], the evaporation-like process of helium atoms, and the formation of solid-like helium structures. These characteristics are expected to be quite general and highly relevant to explain experimental measurements with the newly developed helium droplet mediated deposition technique [7].Peer Reviewe

L'evoluzione demografica del Piemonte : scenari al 1989

Quaderni di ricerca Ires; n. 23- Indice #5- Metodologia di studio e scenari considerati #7- La dinamica demografica del Piemonte #21- L'articolazione comprensoriale dell'evoluzione demografica regionale #43- Analisi demografica dei singoli comprensori #59- Conclusioni #10

Soot inception: A DFT study of σ and π dimerization of resonantly stabilized aromatic radicals

Recent advances in the soot studies have shown experimental evidences of π-radicals and cross-linked structures among the molecular constituents of just-nucleated soot particles. π-radicals could have an important role in particle nucleation by increasing the binding energy between polycyclic aromatic hydrocarbons with respect to pure van der Waals interactions. In this work we use density functional theory by Grimme D3 dispersion correction (DFT-D3) with hybrid functional and localized Gaussian basis set (B3LYP/6-31G**) to analyze and classify the clustering behaviors of two aromatic radicals visualized experimentally by atomic force microscopy (Commodo et al. Combust. Flame 205: 154–164, 2019). These aromatic radicals have different topological structures and delocalization of the unpaired electron. The binding energy and energy bandgap characteristics of the clusters are calculated. The theoretical results show a different clustering behavior for the two aromatic radicals. The one with a partial localization of the unpaired electron tends to form a σ-dimer; conversely, the radical with a greater delocalization of the unpaired electron leads to π-stacking formation with a slight overbinding of few kcal mol−1 with respect to pure van der Waals interactions and a marked lowering of the energy bandgap. The formation of π-stacking induced by delocalized π-radicals could in part explain some spectroscopic evidences observed during soot nucleation. © 2020 Elsevier Lt

Correlation effects in ionic crystals: I. The cohesive energy of MgO

High-level quantum-chemical calculations, using the coupled-cluster approach and extended one-particle basis sets, have been performed for (Mg2+)n (O2-)m clusters embedded in a Madelung potential. The results of these calculations are used for setting up an incremental expansion for the correlation energy of bulk MgO. This way, 96% of the experimental cohesive energy of the MgO crystal is recovered. It is shown that only 60% of the correlation contribution to the cohesive energy is of intra-ionic origin, the remaining part being caused by van der Waals-like inter-ionic excitations.Comment: LaTeX, 20 pages, no figure

Correlation effects in MgO and CaO: Cohesive energies and lattice constants

A recently proposed computational scheme based on local increments has been applied to the calculation of correlation contributions to the cohesive energy of the CaO crystal. Using ab-initio quantum chemical methods for evaluating individual increments, we obtain 80% of the difference between the experimental and Hartree-Fock cohesive energies. Lattice constants corrected for correlation effects deviate by less than 1% from experimental values, in the case of MgO and CaO.Comment: LaTeX, 4 figure

Ground-state properties of rutile: electron-correlation effects

Electron-correlation effects on cohesive energy, lattice constant and bulk compressibility of rutile are calculated using an ab-initio scheme. A competition between the two groups of partially covalent Ti-O bonds is the reason that the correlation energy does not change linearly with deviations from the equilibrium geometry, but is dominated by quadratic terms instead. As a consequence, the Hartree-Fock lattice constants are close to the experimental ones, while the compressibility is strongly renormalized by electronic correlations.Comment: 1 figure to appear in Phys. Rev.

Cohesive properties of alkali halides

We calculate cohesive properties of LiF, NaF, KF, LiCl, NaCl, and KCl with ab-initio quantum chemical methods. The coupled-cluster approach is used to correct the Hartree-Fock crystal results for correlations and to systematically improve cohesive energies, lattice constants and bulk moduli. After inclusion of correlations, we recover 95-98 % of the total cohesive energies. The lattice constants deviate from experiment by at most 1.1 %, bulk moduli by at most 8 %. We also find good agreement for spectroscopic properties of the corresponding diatomic molecules.Comment: LaTeX, 10 pages, 1 figure, accepted by Phys. Rev.