Neural network learned Pauli potential for the advancement of orbital-free density functional theory.

The Pauli kinetic energy functional and its functional derivative, termed Pauli potential, play a crucial role in the successful implementation of orbital-free density functional theory for electronic structure calculations. However, the exact forms of these two quantities are not known. Therefore, perforce, one employs the approximate forms for the Pauli functional or Pauli potential for performing orbital-free density functional calculations.

Structural evolution in gold nanoparticles using artificial neural network based interatomic potentials.

Relativistic effects of gold make its behavior different from other metals. Unlike silver and copper, gold does not require symmetrical structures as the stable entities. We present the evolution of gold from a cluster to a nanoparticle by considering a majority of stable structural possibilities.

A transferable artificial neural network model for atomic forces in nanoparticles.

We have designed a new method to fit the energy and atomic forces using a single artificial neural network (SANN) for any number of chemical species present in a molecular system. The traditional approach for fitting the potential energy surface for a multicomponent system using artificial neural network (ANN) is to consider number of networks for number of chemical species in the system. This shoots the computational cost and makes it difficult to apply to a system containing more number of species.

Correlation of structure with UV-visible spectra by varying SH composition in Au-SH nanoclusters.

In the present work, we model artificial neural network (ANN) potentials for Au (SH) nanoclusters in the range of = 10 to = 38. The accuracy of ANN potentials is tested by comparing the global minimum (GM) structures of Au (SH) nanoclusters, at saturated amount of SH, with the earlier reported structures. The GM structures are reported for the first time for nanoclusters with compositions lower than the saturated SH composition.

c-T phase diagram and Landau free energies of (AgAu) nanoalloy via neural-network molecular dynamic simulations.

For understanding the structure, dynamics, and thermal stability of (AgAu) nanoalloys, knowledge of the composition-temperature (c-T) phase diagram is essential due to the explicit dependence of properties on composition and temperature. Experimentally, generating the phase diagrams is very challenging, and therefore theoretical insight is necessary. We use an artificial neural network potential for (AgAu) nanoalloys.

Spherical harmonics based descriptor for neural network potentials: Structure and dynamics of Au nanocluster.

We propose a highly efficient method for fitting the potential energy surface of a nanocluster using a spherical harmonics based descriptor integrated with an artificial neural network. Our method achieves the accuracy of quantum mechanics and speed of empirical potentials. For large sized gold clusters (Au), the computational time for accurate calculation of energy and forces is about 1.

Structural Evolution of Gold Clusters Au (n = 21-25) Revisited.

We performed a combined theoretical and experimental photoelectron spectroscopy study of the structural evolution of gold anion clusters Au in the size range n = 21-25, a special size range for gold anion clusters where extensive structural changes from the pyramidal structure at Au toward the core-shell structure at Au were expected to occur. Density functional theory calculations with inclusion of spin-orbit effects were employed to produce the simulated spectra for the selected low-energy isomers obtained from basin-hopping global minimum search. The comparison of these simulated spectra with reasonably well-resolved experimental photoelectron spectra resulted in the identification of the low-lying structures of the gold clusters.

Neural network potentials for dynamics and thermodynamics of gold nanoparticles.

For understanding the dynamical and thermodynamical properties of metal nanoparticles, one has to go beyond static and structural predictions of a nanoparticle. Accurate description of dynamical properties may be computationally intensive depending on the size of nanoparticle. Herein, we demonstrate the use of atomistic neural network potentials, obtained by fitting quantum mechanical data, for extensive molecular dynamics simulations of gold nanoparticles.

Methanol clusters (CH3OH)n: putative global minimum-energy structures from model potentials and dispersion-corrected density functional theory.

Putative global minima are reported for methanol clusters (CH3OH)n with n ≤ 15. The predictions are based on global optimization of three intermolecular potential energy models followed by local optimization and single-point energy calculations using two variants of dispersion-corrected density functional theory. Recurring structural motifs include folded and/or twisted rings, folded rings with a short branch, and stacked rings.

Density functional theory guided Monte Carlo simulations: application to melting of Na13.

We present a density functional theory (DFT) based Monte Carlo simulation method in which a simple energy function gets fitted on-the-fly to DFT energies and gradients. The fitness of the energy function gets tested periodically using the classical importance function technique [R. Iftimie, D.

Using swarm intelligence for finding transition states and reaction paths.

We describe an algorithm that explores potential energy surfaces (PES) and finds approximate reaction paths and transition states. A few (≈6) evolving atomic configurations ("climbers") start near a local minimum M1 of the PES. The climbers seek a shallow ascent, low energy, path toward a saddle point S12, cross over to another valley of the PES, and climb down to a new minimum M2 that was not known beforehand.

CO chemisorption on the surfaces of the golden cages.

We report a joint experimental and theoretical study of CO chemisorption on the golden cages. We find that the Au(17)(-) cage is highly robust and retains its cage structure in Au(17)(CO)(-). On the other hand, the Au(16)(-) cage is transformed to a structure similar to Au(17)(-) upon the adsorption of CO.

Structural transition of gold nanoclusters: from the golden cage to the golden pyramid.

How nanoclusters transform from one structural type to another as a function of size is a critical issue in cluster science. Here we report a study of the structural transition from the golden cage Au(16)(-) to the pyramidal Au(20)(-). We obtained distinct experimental evidence that the cage-to-pyramid crossover occurs at Au(18)(-), for which the cage and pyramidal isomers are nearly degenerate and coexist experimentally.

Search for lowest-energy structure of Zintl dianion Si(12)(2-), Ge(12)(2-), and Sn(12)(2-).

We perform an unbiased search for the lowest-energy structures of Zintl dianions (Si(12)(2-), Ge(12)(2-), and Sn(12)(2-)), by using the basin-hopping (BH) global optimization method combined with density functional theory geometric optimization. High-level ab initio calculation at the coupled-cluster level is used to determine relative stabilities and energy ranking among competitive low-lying isomers of the dianions obtained from the BH search. For Si(12)(2-), all BH searches (based on independent initial structures) lead to the same lowest-energy structure Si(12a)(2-), a tricapped trigonal prism (TTP) with C(s) group symmetry.

Ab initio calculation of carbon clusters. II. Relative stabilities of fullerene and nonfullerene C24.

Chemical stabilities of six low-energy isomers of C24 derived from global-minimum search are investigated. The six isomers include one classical fullerene (isomer 1) whose cage is composed of only five- and six-membered rings (56-MRs), three nonclassical fullerene structures whose cages contain at least one four-membered ring (4-MR), one plate, and one monocyclic ring. Chemical and electronic properties of the six C24 isomers are calculated based on a density-functional theory method (hybrid PBE1PBE functional and cc-pVTZ basis set).

Structures and relative stability of neutral gold clusters: Aun (n=15-19).

We performed a global-minimum search for low-lying neutral clusters (Au(n)) in the size range of n=15-19 by means of basin-hopping method coupled with density functional theory calculation. Leading candidates for the lowest-energy clusters are identified, including four for Au(15), two for Au(16), three for Au(17), five for Au(18), and one for Au(19). For Au(15) and Au(16) we find that the shell-like flat-cage structures dominate the population of low-lying clusters, while for Au(17) and Au(18) spherical-like hollow-cage structures dominate the low-lying population.

Lowest-energy structures of water clusters (H2O)11 and (H2O)13.

We employed a four-step searching/screening approach to determine best candidates for the global minima of (H2O)11 and (H2O)13. This approach can be useful when there exist a large number of low-lying and near-isoenergetic isomers, many of which have the same oxygen-skeleton structure. On the two new candidates for the global minimum of (H2O)11, one isomer can be viewed as placing the 11th molecule onto the side of the global minimum of (H2O)10 and the other can be viewed as removing the 12th molecule from the middle layer of the global minimum of (H2O)12.

Evidence of hollow golden cages.

The fullerenes are the first "free-standing" elemental hollow cages identified by spectroscopy experiments and synthesized in the bulk. Here, we report experimental and theoretical evidence of hollow cages consisting of pure metal atoms, Au(n)(-) (n = 16-18); to our knowledge, free-standing metal hollow cages have not been previously detected in the laboratory. These hollow golden cages ("bucky gold") have an average diameter >5.

Relative stability of planar versus double-ring tubular isomers of neutral and anionic boron cluster B20 and B20-.

High-level ab initio molecular-orbital methods have been employed to determine the relative stability among four neutral and anionic B20 isomers, particularly the double-ring tubular isomer versus three low-lying planar isomers. Calculations with the fourth-order Moller-Plessset perturbation theory [MP4(SDQ)] and Dunning's correlation consistent polarized valence triple zeta basis set as well as with the coupled-cluster method including single, double, and noniteratively perturbative triple excitations and the 6-311G(d) basis set show that the double-ring tubular isomer is appreciably lower in energy than the three planar isomers and is thus likely the global minimum of neutral B20 cluster. In contrast, calculations with the MP4(SDQ) level of theory and 6-311+G(d) basis set show that the double-ring anion isomer is appreciably higher in energy than two of the three planar isomers.

Gold-caged metal clusters with large HOMO-LUMO gap and high electron affinity.

We report a series of isoelectronic gold-caged metal clusters, M@Au14 (M = Zr, Hf), and anion clusters, M@Au14- (M = Sc, Y), all having a calculated HOMO-LUMO gap larger than the well-known tetrahedral cluster Au20-the 3D metal cluster with a very large measured HOMO-LUMO gap (1.77 eV). The clusters M@Au14 (M = Sc, Y) also exhibit a calculated electron affinity (EA) and vertical detachment energy (VDE) not only higher than the "superhalogen" icosahedral Al13 cluster but also possibly even higher than a Cl atom which has the highest (measured) elemental EA or VDE (3.

Ab initio calculation of bowl, cage, and ring isomers of C20 and C20-.

High-level ab initio calculations have been carried out to reexamine relative stability of bowl, cage, and ring isomers of C(20) and C(20)(-). The total electronic energies of the three isomers show different energy orderings, strongly depending on the hybrid functionals selected. It is found that among three popular hybrid density-functional (DF) methods B3LYP, B3PW91, PBE1PBE, and a new hybrid-meta-DF method TPSSKCIS, only the PBE1PBE method (with cc-pVTZ basis set) gives qualitatively correct energy ordering as that predicted from ab initio CCSD(T)/cc-pVDZ [CCSD(T)-coupled-cluster method including singles, doubles, and noniterative perturbative triples; cc-pVDZ-correlation consistent polarized valence double zeta] as well as from MP4(SDQ)/cc-pVTZ [MP4-fourth-order Moller-Plesset; cc-pVTZ-correlation consistent polarized valence triple zeta] calculations.

Cooperative effects in two-dimensional ring-like networks of three-center hydrogen bonding interactions.

Cooperative effects in two-dimensional cyclic networks containing intermolecular three-centered hydrogen bonding interactions of the type H1...