Stability and aromaticity of nH2@B12N12 (n=1–12) clusters

Standard ab initio and density functional calculations are carried out to determine the structure, stability, and reactivity of B12N12 clusters with hydrogen doping. To lend additional support, conceptual DFT-based reactivity descriptors and the associated electronic structure principles are also used. Related cage aromaticity of this B12N12 and nH2@B12N12 are analyzed through the nucleus independent chemical shift values

Exohedral complexation of B-39(-) with ECp*+ half-sandwich complexes (E=Si Ge, Sn, Pb): A DFT study

The hexagonal and heptagonal holes of B-39(-) allow its complexation with a half sandwich complex ECp*+ (E=Si, Ge, Sn, Pb). Structure and the nature of bonding of (eta(6/7)-B-39)E(eta(5)-Cp-*) are explored through the density functional theory based computation. (eta(6)-B-39)E(eta(5)-Cp-*) isomers are more stable than (eta(7)-B-39)E(eta(5)-Cp*) and the energy difference between these two isomers decreases down the group from Si to Pb. The dissociation path, (eta(6/7)-B-39)E(eta(5)-Cp-*) -> B-39(-)+ ECp*+ is studied. For all E, (eta(6/7)-B-39)E(eta(5)-Cp-*) is formed exergonically at 298 K temperature as given by the Delta G values of dissociation path [60.1(Si) to 68.3(Pb) kcal/mol for (eta(6)-B-39)E(eta(5)-Cp-*) and 58.3(Si) to 67.8(Pb) kcal/mol for (eta(7)-B-39)E(eta(5)-Cp-*)]. The adduct becomes bent around the central E atom when B-39(-) gets attached to ECp*+ and the amount of bending increases gradually down the group from Si to Pb. Bonding analysis of the stable isomer, (eta(6)-B-39)E(eta 5-Cp*) has been done by natural bonding orbital (NBO) and energy decomposition analyses (EDA). The electron density from B-39(-) is transferred to the ECp*+ moiety as revealed by the NBO analysis. All the complexes are mainly stabilized by the electrostatic and orbital interactions between B-39(-) and ECp*+ fragments as highlighted by the EDA results

A NEW FORM FOR THE KINETIC ENERGY-DENSITY FUNCTIONAL FOR MANY-ELECTRON SYSTEMS

A new simple form for the atomic kinetic energy-density functional (t) is proposed as a sum of the Thomas-Fermi term and a radial correction term, namely, t [p] = (3/10) (3π 2)2/3p5/3 - (1/40)(r.∇ p)/r2, where the first term is the Thomas-Fermi term and p(r) is the Hartree-Fock atomic density. The correction term is part of the -(1/4)∇2p term which occurs in the kinetic energy density; it adds mainly terms of O(Z2) and O(Z5/3) to the Z7/3 atomic Thomas-Fermi energy. The above form generally displays improved local and global behaviour for atomic kinetic energies. Besides satisfying the virial theorem, it gives rise to chemical binding in molecules

Stability analysis of finite-difference schemes for quantum-mechanical equations of motion

For a pdf involving both space and time variables, stability criteria are presently shown to change drastically when the equation contains i, as in the quantum-mechanical equations of motion. It is further noted that the stability of finite difference schemes for quantum-mechanical equations of motion depends on both spatial and temporal zoning. It is possible to compare a free particle Green's function to the solution of a simple diffusion equation, and the quantum-mechanical motion of a free particle to Fresnel diffraction in optics

A (T-P) phase diagram for the adsorption/desorption of carbon dioxide and hydrogen in a Cu(II)-MOF

Solvothermal synthesis of a highly porous metal-organic framework (PMOF) of Cu(II) had been achieved with a bent tetracarboxylate linker, L4- incorporating an -NH2 group in the middle. The design of the linker afforded paddle-wheel secondary building unit (SBU) with metal bound solvent molecules. Upon activation by heating, the overall integrity of the structure remained intact with the result of a PMOF embellished with unsaturated metal centers (UMCs) and free -NH2 groups. This activated PMOF showed adsorption of 6.6% by weight of H-2 gas at 77 K and 62 bar and very high 60% by weight of CO2 gas at 298 K and 32 bar. The adsorption/desorption properties of this MOF has been probed theoretically to obtain additional insights into physisorption of these strategically important gases. The binding energy values reveal the willingness of the CO2 and H-2 gas molecules to get absorbed in Cu(II)-MOF. Temperature-pressure (T-P) phase diagrams have been generated for both of the gas absorption processes at omega B97x-D/TZVP level of theory. Temperature and pressure regions have been identified where Gibbs free energy is negative that is the absorption process is spontaneous. The ab initio molecular dynamics study reveals that the gas saturated Cu(II)-MOFs are stable. Thus this Cu(II)-MOF can be used as an effective gas storage material. (C) 2018 Elsevier Ltd. All rights reserved

Noble Gas Inserted Metal Acetylides (Metal = Cu, Ag, Au)

Metal acetylides (MCCH, M = Cu, Ag, Au) were already experimentally detected in molecular form. Herein, we investigate the possibility of noble gas (Ng) insertion within the C-H bond of MCCH and their stability is compared with those of the reported MNgCCH and HCCNgH molecules. Our coupled-cluster-level computations show that MCCNgH (Ng = Kr, Xe, Rn) systems are local minima on the corresponding potential energy surfaces, whereas their lighter analogues do not remain in the chemically bound form. Further, their stability is analyzed with respect to all possible dissociation channels. The most favorable dissociation channel leads to the formation of free Ng and MCCH. However, there exists a high free energy barrier (29.3-46.9 kcal/mol) to hinder the dissociation. The other competitive processes against their stability include two-body and three-body neutral dissociation channels, MCCNgH -> MCC + NgH and MCCNgH -> MCC + Ng + H, respectively, which are slightly exergonic in nature at 298 K for Ng = Kr, Xe and M = Cu, Ag, and for AuCCKrH. However, the Xe analogues for Cu and Ag and AuCCKrH would be viable at a lower temperature. AuCCNgH (Ng = Kr-Rn) molecules are the best candidates for experimental realization, since they have higher dissociation energy values and higher kinetic protection in the case of feasible dissociation channels compared to the Cu and Ag systems. A detailed bonding analysis indicates that the Ng-H bonds are genuine covalent bonds and there is also a substantial covalent character in Ng-C contacts of these molecules. Moreover, the possibility of insertion of two Xe atoms in AuCCH resulting in AuXeCCXeH and the stability of XeAuXeCCXeH are also tested herein