The structural, electronic and magnetic properties of Con clusters (n =2−20) have been investigated using density functional theory within the pseudopotential plane wave method. An unusual hexagonal growth pattern has been observed in the intermediate size range, n =15−20. The cobalt atoms are ferromagnetically ordered and the calculated magnetic moments are found to be higher than that of corresponding hcp bulk value, which are in good agreement with the recent SternGerlach experiments. The average coordination number is found to dominate over the average bond length to determine the effective hybridization and consequently the cluster magnetic moment.

We systematically investigate the structural, electronic and magnetic properties of Mnn clusters (n = 2−20) within the ab-initio pseudopotential plane wave method using generalized gradient approximation for the exchange-correlation energy. A new kind of icosahedral structural growth has been predicted in the intermediate size range. Calculated magnetic moments show an excellent agreement with the Stern-Gerlach experiment. A transition from ferromagnetic to ferrimagnetic Mn−Mn coupling takes place at n = 5 and the ferrimagnetic states continue to be the ground states for the entire size range. Possible presence of multiple isomers in the experimental beam has been argued. No signature of non-metal to metal transition is observed in this size range and the coordination dependence of d−electron localization is discussed.

In this paper we propose a tight-binding molecular dynamics with parameters fitted to firstprinciples calculations on the smaller clusters and with an environment correction, to be a powerful technique for studying large transition/noble metal clusters. In particular, the structure and stability of Cun clusters for n = 3−55 are studied by using this technique. The results for small Cun clusters (n = 3 − 9) show good agreement with ab initio calculations and available experimental results. In the size range 10 ≤ n ≤ 55 most of the clusters adopt icosahedral structure which can be derived from the 13-atom icosahedron, the polyicosahedral 19-, 23-, and 26-atom clusters and the 55-atom icosahedron, by adding or removing atoms. However, a local geometrical change from icosahedral to decahedral structure is observed for n = 40 − 44 and return to the icosahedral growth pattern is found at n = 45 which continues. Electronic "magic numbers" (n = 2, 8, 20, 34, 40) in this regime are correctly reproduced. Due to electron pairing in HOMOs, even-odd alternation is found. A sudden loss of even-odd alternation in second difference of cluster binding energy, HOMO-LUMO gap energy and ionization potential is observed in the region n ∼ 40 due to structural change there. Interplay between electronic and geometrical structure is found.

Inducing magnetic moment in otherwise nonmagnetic two-dimensional semiconducting materials is the key first step to design spintronic materials. Here, we study the absorption of transition-metals on pristine and defected single-layer phosphorene, within density functional theory. We predict that increased transition-metal diffusivity on pristine phosphorene would hinder any possibility of controlled magnetism, and thus any application. In contrast, the point-defects will anchor metals, and exponentially reduce the diffusivity. Similar to other two-dimensional materials, metals bind strongly on both pristine and defected phosphorene, and we provide a microscopic description of bonding, which explain the qualitative trend with increasing number of valence electrons. We further argue that the divacancy complex is imperative in any practical purpose due to their increased thermodynamic stability over monovacancy. For most cases, the defecttransition metal complexes retain the intrinsic semiconduction properties, and also induce a local magnetic moment with large exchangesplitting and spin-flip energies, which are necessary for spintronic applications. Specifically, the V/Mn/Fe absorbed at the divacancy have tremendous promise in this regard. Further, we provide a simple microscopic model to describe the local moment formation in these transition metal and defect complexes. We also note that metal absorption may completely alter the intrinsic semiconducting nature and give rise to half-metallic and metallic composite system.

Here we report kinetic Monte Carlo simulations of dislocation climb in heavily deformed, body-centered cubic iron comprising a supersaturation of vacancies. This approach explicitly incorporates the effect of nonlinear vacancy-dislocation interaction on vacancy migration barriers as determined from atomistic calculations, and enables observations of diffusivity and climb over time scales and temperatures relevant to power-law creep. By capturing the underlying microscopic physics, the calculated stress exponents for steady-state creep rates agree quantitatively with the experimentally measured range, and qualitatively with the stress dependence of creep activation energies.

Earth-abundant quaternary chalcogenides are promising candidate materials for thin-film solar cells. Here we have synthesized Cu2NiSnS4 nanocrystals and thin films in a novel zincblende type cubic phase using a facile hot-injection method. The structural, electronic, and optical properties are studied using various experimental techniques, and the results are further corroborated within first-principles density functional theory based calculations. The estimated direct band gap ∼ 1.57 eV and high optical absorption coefficient ∼ 106 cm–1 indicate potential application in a low-cost thin-film solar cell. Further, the alignments for both conduction and valence bands are directly measured through cyclic voltametry. The 1.47 eV electrochemical gap and very small conduction band offset of −0.12 eV measured at the CNTS/CdS heterojunction are encouraging factors for the device. These results enable us to model carrier transport across the heterostructure interface. Finally, we have fabricated a CNTS solar cell device for the first time, with high open circuit voltage and fill factor. The results presented here should attract further studies.

An ordered self-assembly of CsPbBr quantum dots (QDs) was generated on the surface of few-layer black phosphorus (FLBP). Strong quenching of the QD fluorescence was observed, and analyzed by time-resolved photoluminescence (TR-PL) studies, DFT calculations, and photoconductivity measurements. Charge transfer by type I band alignment is suggested to be the cause of the observed effects.

We explore possible ways to manipulate the intrinsic edge magnetism in hexagonal graphene nanoflake with zigzag edges, using density functional theory supplemented with on-site Coulomb interaction. The effect of carrier doping, chemical modification at the edge, and finite temperature on the edge magnetism has been studied. The magnetic phase diagram with varied carrier doping, and on-site Coulomb interaction is found to be complex. In addition to the intrinsic antiferromagnetic solution, as predicted for charge neutral hexagonal nanoflake, fully polarized ferromagnetic, and mixed phase solutions are obtained depending on the doped carrier concentration, and on-site Coulomb interaction. The complexity arises due to the competing nature of local Coulomb interaction and carrier doping, favoring antiferromagnetic and ferromagnetic coupling, respectively. Chemical modification of the edge atoms by hydrogen leads to partial quenching of local moments, giving rise to a richer phase diagram consisting of antiferromagnetic, ferromagnetic, mixed, and nonmagnetic phases. We further report the influence of temperature on the long-range magnetic ordering at the edge using ab initio molecular dynamics. In agreement with the recent experimental observations, we find that temperature can also alter the magnetic state of neutral nanoflake, which is otherwise antiferromagnetic at zero temperature. These findings will have important implications in controlling magnetism in graphene based low dimensional structures for technological purpose, and in understanding varied experimental reports.