We present an approach to calculate total energies of nanoclusters based on first principles estimates. For very large clusters the total energy can be separated into surface, edge and corner energies, in addition to bulk contributions. Using this separation and estimating these with direct, first principles calculations, together with the relevant chemical potentials, we have calculated the total energies of Cu and CdSe tetrahedrons containing a large number of atoms. In our work we consider polyhedral clusters so that in addition our work provides direct information on relaxation. For Cu the effects are very small and the clusters vary uniformly from very small to very large sizes. For CdSe there are important variations in surface and edge structures for specific sizes; nevertheless, the approach can be used to extrapolate to large non-stoichiometric clusters with polar surfaces.
High-performance materials rely on small reorganization energies to facilitate both charge separation and charge transport. Here, we performed DFT calculations to predict small reorganization energies of rectangular silicene nanoclusters with hydrogen-passivated edges denoted by H-SiNC. We observe that across all geometries, H-SiNCs feature large electron affinities and highly stabilized anionic states, indicating their potential as n-type materials. Our findings suggest that fine-tuning the size of H-SiNCs along the zigzag and armchair directions may permit the design of novel n-type electron…
Ionization threshold energies of Al$_n$ (n=32-95) nanoclusters are determined by laser ionization of free neutral metal clusters thermalized to several temperatures in the range from 65 K to 230 K. The photoion yield curves of cold clusters follow a quadratic energy dependence above threshold, in agreement with the Fowler law of surface photoemission. Accurate data collection and analysis procedures make it possible to resolve very small (few parts in a thousand) temperature-induced shifts in the ionization energies. Extrapolation of the data to the bulk limit enables a determination of the th…
Numerical calculations of surface and volume plasma excitations in silicon and silicon-hydrogen nanoclusters in the range Si$_{10}$-Si$_{60}$ and Si$_3$H$_8$-Si$_{39}$H$_{40}$ are performed. Some nanocluster structures were obtained using the evolutionary algorithm, others were taken from the database. The GW method was used to calculate the response function and self-energy of the structures under study. The applied method shows the results consistent with the experiment (except plasmaron artifacts) and sufficient sensitivity allowing to investigate the effect of the cluster structure and siz…
Evolutionary algorithm is combined with full-potential ab-initio calculations to investigate conformational space of (MoS$_2$)$_n$ and (MoSe$_2$)$_n$ (n=1-10) nanoclusters and to identify the lowest energy structural isomers of these systems. It is argued that within both BLYP and PBE functionals, these nanoclusters favor sandwiched planar configurations, similar to their ideal planar sheets. The second order difference in total energy ($Δ_2$E) of the lowest energy isomers are computed to estimate the abundance of the clusters at different sizes and to determine the magic sizes of (MoS$_2$)$_n…
Surface morphology of size-selected silver nanocluster films grown by dc magnetron sputtering has been investigated by means of an atomic force microscopy (AFM). From the height-height correlation functions ( HHCF) obtained from corresponding AFM images, the scaling exponents are calculated and two types of growth regimes have been observed. In the first regime, the growth exponent is found to be \b{eta}1 = 0.27\pm0.07 close to the KPZ growth exponent, while in the second growth regime shadowing effect plays dominant role which gives the growth exponent value \b{eta}2 = 0.88\pm0.28. On the oth…
Conventional Oxide dispersion strengthened steels are characterized by thermally stable, high density of Y-Ti-O nanoclusters, which are responsible for their high creep strength. Ti plays a major role in obtaining a high density of ultrafine particles of optimum size range of 2-10 nm. In Al-containing ODS steels developed for corrosion resistance, Y-Al-O clusters formed are of size range 20 -100 nm, and Ti fails in making dispersions finer in the presence of Al. Usage of similar alloying elements like Zr in place of Ti is widely considered. In this study, binding energies of different stages o…
First-Principles Investigation of Ammonia Adsorption and N-H Activation on W-B Nanoclusters
Skolkovo Institute of Science and Technology（斯科尔科沃科学技术研究所）；King Fahd University of Petroleum and Minerals（法赫德国王石油与矿产大学）；National Research University Higher School of Economics (HSE University)（国立高等经济大学）
Classical molecular dynamics simulation with embedded atom method potential had been performed to investigate the surface structure and solidification morphology of aluminum nanoclusters Aln (n = 256, 604, 1220 and 2048). It is found that Al cluster surfaces are comprised of (111) and (001) crystal planes. (110) crystal plane is not found on Al cluster surfaces in our simulation. On the surfaces of smaller Al clusters (n = 256 and 604), (111) crystal planes are dominant. On larger Al clusters (n = 1220 and 2048), (111) planes are still dominant but (001) planes can not be neglected. Atomic den…
Teaching a Transformer to Think Like a Chemist: Predicting Nanocluster Stability
Federal University of Pelotas（佩洛塔斯联邦大学）；Hamburg University of Technology（汉堡工业大学）；University of Brasília（巴西利亚大学）；Federal University of Paraná（巴拉那联邦大学）；Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）
We review the theory behind abundance of experimentally observed nanoclusters produced in beams, aiming to understand their magic number behavior. It is shown how use of statistical physics, with certain assumptions, reduces the calculation of equilibrium abundance to that of partition functions of single clusters. Methods to practically calculate these partition functions are introduced. As an illustration, we compute the abundance of Lennard-Jones clusters at low temperatures, which reveals their experimentally observed magic number behavior. We then briefly review kinetic approach to the pr…
Molecular dynamics simulations using empirical force fields (EFFs) are crucial for gaining fundamental insights into atomic structure and long timescale dynamics of Au nanoclusters with far-reaching applications in energy and devices. This approach is thwarted by the failure of currently available EFFs in describing the size-dependent dimensionality and diverse geometries exhibited by Au clusters (e.g., planar, hollow cages, pyramids). Owing to their ability to account for bond directionality, bond-order based EFFs, such as the Tersoff-type Bond Order Potential (BOP), are well suited for such …
The geometric and electronic properties of Bi-adsorbed monolayer graphene, enriched by the strong effect of substrate, are investigated by first-principles calculations. The six-layered substrate, corrugated buffer layer, and slightly deformed monolayer graphene are all simulated. Adatom arrangements are thoroughly studied by analyzing the ground-state energies, bismuth adsorption energies, and Bi-Bi interaction energies of different adatom heights, inter-adatom distance, adsorption sites, and hexagonal positions. A hexagonal array of Bi atoms is dominated by the interactions between the buffe…
Methylammonium lead triiodide (CH3NH3PbI3) perovskite solar cell is a gem in the list of photovoltaic semiconductors. Although there are numerous fundamental and technological questions yet to be addressed covering various aspects of this system for its commercialization, this study has employed first-principles DFT to model the [PbI6(CH3NH3)n]m zero-dimensional nanoclusters. Using the calculated binding energy landscapes, it has answered the question: why the corner-sharing PbI6 octahedron is surrounded by eight units of the organic cation in the large-scale supramolecular structures of the C…
A general method is presented to calculate absolute binding energies of core levels in metals and insulators, based on a penalty functional and an exact Coulomb cutoff method in a framework of the density functional theory. The spurious interaction of core holes between supercells is avoided by the exact Coulomb cutoff method, while the variational penalty functional enables us to treat multiplet splittings due to chemical shift, spin-orbit coupling, and exchange interaction on equal footing, both of which are not accessible by previous methods. It is demonstrated that the absolute binding ene…
Determining accurate absolute surface energies for polar surfaces of semiconductors has been a great challenge in decades. Here, we propose pseudo-hydrogen passivation to calculate them, using density functional theory approaches. By calculating the energy contribution from pseudo-hydrogen using either a pseudo molecule method or a tetrahedral cluster method, we obtained (111) surfaces energies of Si, GaP, and ZnS with high self-consistency. This method quantitatively confirms that surface energy is determined by the number and the energy of dangling bonds of surface atoms. Our findings may gr…
We present a method of extracting the exchange parameters of the classical Heisenberg model from first-principles calculations of spin-spiral total energies based on density functional theory. The exchange parameters of the transition-metal monoxides MnO and NiO are calculated and used to estimate magnetic properties such as transition temperatures and magnon energies. Furthermore we show how to relate the magnon energies directly to differences in spin-spiral total energies for systems containing an arbitrary number of magnetic sublattices. This provides a comparison between magnon energies u…
The ground state energies of Ag and Au in the face-centered cubic (FCC), body-centered cubic (BCC), simple cubic (SC) and the hypothetical diamond-like phase, and dimer were calculated as a function of bond length using density functional theory (DFT). These energies were then used to parameterize the many-body Gupta potential for Ag and Au. This parameterization over several phases of Ag and Au was performed to guarantee transferability of the potentials and to make them appropriate for studies of related nanostructures. Depending on the structure, the energetics of the surface atoms play a c…
The Energetics of Li Off-Centering in K$_{1-x}$Li$_x$TaO$_3$; First Principles Calculations
K $_{1-x}$ Li $_{x}$ TaO $_3$（KLT）固溶体表现出与Li离子从理想钙钛矿A位位置的大位移有关的各种有趣的物理现象。采用第一性原理计算研究了KLT超原胞的这些现象。晶格动力学计算KLT表现出Li偏心不稳定性。计算了孤立Li离子和Li-Li对到第四邻体的Li位移的能量。在Li-Li对中，最近邻Li离子之间的相互作用强烈地有利于沿着对轴的铁电对准。这种Li-Li对可以被认为是KLT中极性纳米团簇的“种子”。电致伸缩，局部氧弛豫，耦合到KT软模式，并与邻近的锂离子的相互作用都增强了从Li偏心的极化。孤立的锂离子和最近邻的锂-锂对的跳跃势垒的计算结果与Arcidius拟合实验介电数据吻合得很好。
The ground-state correlation energy calculated in the random-phase approximation (RPA) is known to be identical to that calculated using a subset of terms appearing in coupled-cluster theory with double excitations. In particular, this equivalence requires keeping only those terms that generate time-independent ring diagrams, in the Goldstone sense. Here I show that this equivalence extends to neutral excitation energies, for which those calculated in the RPA are identical to those calculated using an approximation to equation-of-motion coupled-cluster theory with double excitations (EOM-CCD).…
We propose a method to decompose the total energy of a supercell containing defects into contributions of individual atoms, using the energy density formalism within density functional theory. The spatial energy density is unique up to a gauge transformation, and we show that unique atomic energies can be calculated by integrating over Bader and charge-neutral volumes for each atom. Numerically, we implement the energy density method in the framework of the Vienna ab initio simulation package (VASP) for both norm-conserving and ultrasoft pseudopotentials and the projector augmented wave method…
