Cohesive Energy Of Solid Research Articles

Electronic structure and cohesive energy of silylmethyl fullerene and methanoindene fullerene solids

Using the density functional theory, we studied the energetics and electronic structures of chemically decorated fullerene solids, monoclinic phases of silylmethyl fullerene (SIMEF) and methanoindene fullerene (MIF), under the experimentally determined lattice parameters. Cohesive energies of these solids are 1.83 and 1.07 eV for SIMEF and MIF, respectively, despite the large intermolecular spacing owing to the functional groups. The SIMEF and MIF solids are semiconductors with a moderate band gap of about 1.2 eV with narrow dispersion band near the band gap. We also elucidated that these solids exhibit a strong anisotropic band dispersion relation near the gap, because of their large asymmetric molecular shape. The calculated electron effective masses range from 1.37me to 7.91me for the SIMEF solid and from 0.57me to 4.23me for the MIF solid.

Rungs 1 to 4 of DFT Jacob's ladder: Extensive test on the lattice constant, bulk modulus, and cohesive energy of solids.

A large panel of old and recently proposed exchange-correlation functionals belonging to rungs 1 to 4 of Jacob's ladder of density functional theory are tested (with and without a dispersion correction term) for the calculation of the lattice constant, bulk modulus, and cohesive energy of solids. Particular attention will be paid to the functionals MGGA_MS2 [J. Sun et al., J. Chem. Phys. 138, 044113 (2013)], mBEEF [J. Wellendorff et al., J. Chem. Phys. 140, 144107 (2014)], and SCAN [J. Sun et al., Phys. Rev. Lett. 115, 036402 (2015)] which are meta-generalized gradient approximations (meta-GGA) and are developed with the goal to be universally good. Another goal is also to determine for which semilocal functionals and groups of solids it is beneficial (or not necessary) to use the Hartree-Fock exchange or a dispersion correction term. It is concluded that for strongly bound solids, functionals of the GGA, i.e., rung 2 of Jacob's ladder, are as accurate as the more sophisticated functionals of the higher rungs, while it is necessary to use dispersion corrected functionals in order to expect at least meaningful results for weakly bound solids. If results for finite systems are also considered, then the meta-GGA functionals are overall clearly superior to the GGA functionals.

Assessment of the TCA functional in computational chemistry and solid-state physics

We assess the Tognetti–Cortona–Adamo (TCA) generalized gradient approximation correlation functional (Tognetti et al. in J Chem Phys 128:034101, 2008) for a variety of electronic systems. We find that, even if the TCA functional is not exact for the uniform electron gas, it is very accurate for the jellium surface correlation energies and it gives a realistic description of the quantum oscillations and surface effects of various jellium clusters that are important model systems in computational chemistry and solid-state physics. When the TCA correlation is combined with the non-empirical PBEint, Wu-Cohen, and PBEsol $$_b$$ exchange functionals, the resulting exchange–correlation approximations provide good performances for a broad palette of systems and properties, being reasonably accurate for thermochemistry and geometry of molecules, transition metal complexes, non-covalent interactions, equilibrium lattice constants, bulk moduli, and cohesive energies of solids.

Per‐Olov Löwdin curriculum vitae

Per‐Olov Löwdin curriculum vitae

Generalized-gradient approximations to density-functional theory: A comparative study for atoms and solids.

Pseudopotential calculations within density-functional theory for a few selected solids (Si, GaAs, and Al) are used to assess the validity of two generalized-gradient approximations (GGA's), the one proposed by Becke and Perdew (BP) and the more recent one proposed by Perdew and Wang (PW) in comparison with the currently used local-density approximation (LDA). The GGA's give total energies of atoms and cohesive energies of solids that are closer to experiment than the LDA results. Lattice constants are reproduced with the same accuracy as in LDA, while bulk moduli and zone-center phonon frequencies are underestimated with respect to both the LDA and the experimental values. Comparison to all-electron results shows that in both GGA schemes the validity of the pseudopotential approach is as good as in LDA. The predictions of the two GGA's are similar, the PW functional yielding results marginally, but systematically, closer to experiment. The calculated values of the transition pressure in Si between the diamond and the beta-tin structure are 72 kbar (LDA), 164 kbar (BP), and 135 kbar (PW), to be compared with the two available experimental values of 103 and 125 kbar.

A comparison between high- and low-energy ion mixing at different temperatures

High-energy ion mixing occurs when an ion beam of a few hundred keV bombards an interface under the surface. Low-energy ion mixing arises when an ion beam of a few keV bombards an interface near the surface during, e.g., sputter depth profiling and low-energy ion-assisted deposition. At low temperatures, the rate of both high- and low-energy ion mixing can be influenced by thermodynamic parameters, such as the heat of mixing and the cohesive energy of solids. These effects are demonstrated by ion mixing experiments using metallic bilayers consisting of high-atomic-number elements. A model of diffusion in thermal spikes is used to explain this similarity. Low-energy ion mixing can also be strongly affected by surface diffusion and the morphological stability of thin films. These effects are illustrated using results obtained from sputter depth profiling of Ag/Ni, Ag/Fe, and Ag/Ti bilayers at elevated temperatures. High-energy ion mixing at low temperatures can be influenced by the anisotropic momentum distribution in a collision cascade as seen from a set of marker experiments to determine the dominant moving species in high-energy ion mixing. An understanding of these similarities and differences between high- and low-energy ion mixing at different temperatures will provide useful guidelines for applications of ion mixing.

Similarities and Differences in the Mechanisms of High and Low Energy Ion Mixing

AbstractHigh energy ion mixing occurs when an ion beam of a few hundred keV bombards an interface under the surface. Low energy ion mixing arises when an ion beam of a few keV bombards an interface near the surface during, for example, sputter depth profiling and low energy ion assisted deposition. At low temperatures, the rate of both high and low energy ion mixing can be influenced by thermodynamic parameters, such as the heat of mixing and the cohesive energy of solids. These effects are demonstrated by ion mixing experiments using metallic bilayers consisting of high atomic number elements. A model of diffusion in thermal spikes is used to explain this similarity. Low energy ion mixing can also be strongly affected by surface diffusion and the morphological stability of thin films. These effects are illustrated using results obtained from sputter depth profiling of Ag/Ni bilayers at elevated temperatures. High energy ion mixing at low temperatures can be influenced by the anisotropic momentum distribution in a collision cascade as seen from a set of marker experiments to determine the dominant moving species in high energy ion mixing. These similarities and differences between high and low energy ion mixing illustrate the diversity of ion-solid interactions.

Search for Simplicity: The cohesive energy of solids

Search for Simplicity: The cohesive energy of solids

Molecular Dissociation and Reconstitution on Solids

The dependence of heterogeneous reactions on the nature of the solid surface is explored by analyzing the elementary rate processes involved. The relations between the rates of adsorption, surface diffusion, and evaporation, and the depth and distribution of binding sites on the surface are presented. Empirical generalizations concerning the binding energy of adatoms and the cohesive energy of solids are examined; Pauling's additivity rule is found to fail for most metal hydrides and thus does not provide a reliable base for estimating the covalent contribution to the heat of adsorption. Rates of association of atoms and dissociation of molecules on solids are estimated from a knowledge of the experimental heat of adsorption — ΔH and the postulate that the activated complex for dissociative chemisorption of a diatom has a configuration resembling two noninteracting atoms, one in its equilibrium binding position on the surface, the other in the saddle-point position for surface migration. For chemisorption on clean metals, it is found that an activation energy can be expected only for systems in which the heat of adsorption is small (— ΔH <10 kcal/mole), in agreement with experiment. Conversely, desorption of diatoms by combination of atoms deposited in excess of the equilibrium amounts on metals on which — ΔH <0 is limited only by surface diffusion and therefore should occur rapidly, as is observed. The mechanism of heterogeneous recombination of atoms is outlined; it is shown that for hydrogen atoms only small variations in the efficiency of this process on different metals are expected at pressures of the monatomic gas less than 10—3 mm, and that these are primarily dictated by the rate of direct recombination between gas phase and adsorbed atoms. For metals on which chemisorption from the molecular gas is endothermic, the recombination coefficient should approach unity above room temperature. In the converse process, the dissociation of diatomic molecules into atoms at a hot metal surface, variations in the rate of atomization may occur for different metals; for those on which adsorption is endothermic the rate should be small since it is the adsorption step which results in specificity. The rate of atomization is also shown to depend upon the first power of the pressure of the molecular gas p2 in the region of low pressures, changing to a dependence on p2½ at higher pressures where encounters between adsorbed atoms become limiting. The same picture of the activated complex for chemisorption is applied to the interaction of gases with nonmetals. From the appreciable activation energy observed for adsorption of diatoms on nonmetals, it is concluded that binding sites on these surfaces are widely separated. This suggests that dissociation or excitation of the gas-phase molecule to a higher vibrational state should increase the rate of adsorption, and conversely that the recombination efficiency of nonmetals for atoms should be small. These expectations are found to be in agreement with experiment.