Simple Metal Atoms Research Articles

Rational design of super-alkalis and their role in CO2 activation.

Super-alkalis are clusters of atoms. With ionization potentials smaller than those of the alkali atoms, they are playing an increasing role in chemistry as highlighted by recent applications in solar cells as well as in Li-ion batteries. For the past 40 years superalkalis were designed using inorganic elements with the sp orbital character. Here, we show that a large class of superalkalis composed of only simple metal atoms, transition metal complexes as well as organic molecules can be designed by making use of electron counting rules beyond the octet rule. Examples include Al3+, Mn(B3N3H6)2+, B9C3H12+, and C5NH6+ which obey the jellium shell closure rule, the 18-electron rule, the Wade-Mingos rule, and Hückel's aromatic rule, respectively. We further show that the ability of superalkalis to transfer an electron easily can be used to activate a CO2 molecule by transforming it from a linear to a bent structure. These results, based on density functional theory with generalized gradient approximation for exchange-correlation potential, open the door to a new class of catalysts for CO2 activation.

Substitutional impurities influence on hydrogen sorption properties of titanium and zirconium

The influence of substitutional impurities on the hydrogen absorption energy in Ti and Zr is investigated by the projector augmented wave method within the density functional theory. Obtained results demonstrate that simple metal atoms are repulsive to H, whereas transition metal atoms attract H and provide traps for H. The relationship between the interaction energy, the lattice distortion and the electronic structure of metals is analyzed.

Stability and Spectroscopic Properties of Singly and Doubly Charged Anions

Using density functional theory and hybrid B3LYP exchange-correlation energy functional we have studied the structure, stability, and spectroscopic properties of singly and doubly charged anions composed of simple metal atoms (Na, Mg, Al) decorated with halogens such as Cl and pseudohalogens such as CN. Since pseudohalogens mimic the chemistry of halogen atoms, our objective is to see if pseudohalogens can also form superhalogens much as halogens do and if the critical size for a doubly charged anion depends upon the ligand. The electron affinities of MCl(n) (M = Na, Mg, Al) exceed the value of Cl for n ≥ (k + 1), where k is the normal valence of the metal atom. However, for M(CN)(n) complexes this is only true when n = k + 1. In addition, while the electron affinities and vertical detachment energies of MCl(n) complexes are close to each other, they are markedly different when Cl is replaced by pseudohalogen, CN. The origin of these anomalous results is found to be due to the large binding energy of cyanogen, (NCCN) molecule. Because of the tendency of CN molecules to dimerize, the ground state geometries of the neutral and anionic M(CN)(n) complexes are very different when their number exceed the normal valence of the metal atom. While our calculations support the conclusion of Skurski and co-workers that pseudohalogens can form the building blocks of superhalogens, we show that there is a limitation on the number of CN moieties where this is true. Equally important, we find large differences between the ground state geometries of the neutral and anionic M(CN)(n) complexes for n ≥ (k + 2) which could play an important role in interpreting future experimental data on M(CN)(n) complexes. This is because the electron affinity defined as the energy difference between the ground states of the anion and neutral can be very different from the adiabatic detachment energy defined as the energy difference between the ground state of the anion and its structurally similar neutral isomer.

Doping induced magnetic transition in Mn-based molecular systems

Using density functional theory with generalized gradient approximation for exchange and correlation potential we show that the magnetic coupling between Mn atoms in Mn2Cln molecular systems can be manipulated not only by varying the number of Cl atoms but also by doping simple metal atoms such as Li and Mg. The switching between antiferromagnetic to ferromagnetic couplings is brought about by competition between double exchange and superexchange mechanisms. Ability to control the magnetic coupling in molecular systems can have technological potential for future microelectronics.

Magic Rule forAlnHmMagic Clusters

Using the electronic shell closure criteria, we propose a new electron counting rule that enables us to predict the size, composition, and structure of many hitherto unknown magic clusters consisting of hydrogen and aluminum atoms. This rule, whose validity is established through a synergy between first-principles calculations and anion-photoelectron spectroscopy experiments, provides a powerful basis for searching magic clusters consisting of hydrogen and simple metal atoms.

First-principles investigations of ordering in binary α-Ti solid solutions

The ordering tendency in binary f-Ti solid solution containing 3sp or 4sp simple-metal (SM) or 3d transition-metal (TM) solute is investigated systematically by the linear muffin-tin orbital (LMTO) method within the atomic sphere approximation (ASA). We demonstrated that the effective pairwise interaction (EPI) energy in a solid solution is equal to half the solute-solute interaction energies and can be evaluated by a supercell total energy approach. The calculations of EPI energy both with and without volume relaxation of the supercells and local density of states (LDOS) show that the EPI energies of Ti-SM and Ti-TM solutions are dominated by different factors. For Ti-SM solutions, the EPI energies are of large absolute values with a negative sign, indicating strong ordering tendency in these solutions. The volume relaxation does not alter the EPI energy substantially. The calculated LDOS shows that the ordering tendency in Ti-SM solutions may be related to the hybridization between the electrons of the SM atoms when they are close to each other. For most Ti-TM solutions, if calculated without relaxation, the absolute EPI energies are very small; however, if calculated with relaxation, they are of relatively large positive values, indicating a clustering tendency in these solutions. By combining the calculated EPI energy and Flinn's model for short-range order (SRO) strengthening, the increase in critical shear stress sro due to SRO is estimated for Ti-SM alloys, and the results qualitatively agree with experiment.

First-principles investigation of solute-hydrogen interaction in a α-Ti solid solution

In this paper, a first-principles method is used to calculate the interaction energy between substitutional solute atoms and hydrogen in alpha-Ti. The results show that simple metal (SM) solute atoms are repulsive to H and therefore are detraps for H, whereas transition metal (TM) solute atoms, with smaller sizes than that of the host atoms, attract H and provide traps for H. The relationship between the interaction energy and lattice distortion as well as the electronic structure is investigated. The SM-H and TM-H interactions are dominated by different factors. The repulsive interaction between SM atoms and H is mainly due to the hybridization between the electrons of SM atoms and H when they are close to each other. The interaction between the TM solutes and H is attributable to the atomic size effect, and can be described satisfactorily by Matsumoto's strain field relaxation model. From the solute-H interaction energy and available measured terminal solubility of hydrogen (TSH), the relationship between the solute trapping of hydrogen and TSH in alpha-Ti is discussed. No coherent relationship is found between the theoretical hydrogen trapping effect and the experimental TSH in alpha-Ti alloys.

ATOMICCLUSTERS AS ABRANCHOFNUCLEARPHYSICS

▪ Abstract The conduction electrons in clusters of simple metal atoms are approximatively independent and free. Nucleons in nuclei also behave as delocalized and independent fermions. This generic behavior generates analogies between metal clusters and nuclei, such as the shell structure, the shapes, and the dipole vibration mode. However, there are also major differences that arise from the presence of ions in metal clusters. Fission of nuclei and clusters, and particle emission from them, reveal these differences.

Ab initio molecular dynamics via density based energy functionals

The use of energy functionals based on charge density as the basic variable is advocated for ab initio molecular dynamics. It is demonstrated that the constraint of positivity of density can be incorporated easily by using the square root of the density for minimization of the energy functional. An ad hoc prescription for including non-local pseudopotentials for plane wave based calculations is proposed and is shown to yield improved results. Applications are reported for equilibrium geometries of small finite systems, viz. dimers and trimers of simple metal atoms like Na and Mg, which represent a rather stringent test for approximate kinetic energy functionals involved in such calculations.

Initial investigation of the homogeneous nucleation of cesium vapor

Initial measurements of the homogeneous nucleation of supersaturated cesium vapors using an upward thermal diffusion cloud chamber specially designed for use with highly reactive materials are presented. Comparison of the supersaturations measured at higher temperatures (greater than 455 K) with the supersaturations predicted by Classical nucleation theory show for the first time that the nucleation behavior of simple normal metals can be described by Classical theory. This agreement implies that the description of relatively large clusters of simple metal atoms (more than 25 atoms) as small liquid droplets with bulk metallic properties is valid. However, as the temperature decreases below 455 K, an increasingly larger supersaturation than that predicted by theory is required. This deviation from theory is so sharp that by 430 K the difference is an order of magnitude, and below 420 K nucleation cannot be observed. The deviation is discussed in the context of loss of bulk metallic properties with decreasing critical nuclei size. Other possible reasons for a deviation towards larger supersaturations are also considered.

A new simple pseudopotential with applications to liquid metal structure factor calculations

The self-consistent fields for 24 simple metal atoms have been calculated and unscreened so as to obtain the electron-ion potentials. The results, to good accuracy, take the form - (z/r) [1 + a exp(− br)] from well below the Ashcroft radius r c to well above it, and the parameters a,b show systematic, physically interpretable trends. It will sometimes be profitable to generalise the Ashcroft pseudopotential so as to incorporate explicitly the above ionic tail. Thus, a simple local form can be retained with a wider range of applicability. Concentration fluctuations in liquid NaCs are used to illustrate the point.