Shiv N. Khanna

Bio: Shiv N. Khanna is an academic researcher from Virginia Commonwealth University. The author has contributed to research in topics: Cluster (physics) & Electronic structure. The author has an hindex of 56, co-authored 368 publications receiving 14398 citations. Previous affiliations of Shiv N. Khanna include University of Pennsylvania & National Autonomous University of Mexico.

Cluster-Assembled Materials

Abstract: Cluster-assembled materials offer the ability to tune component properties, lattice parameters, and thus coupling of physical properties through the careful selection and assembly of building blocks. Multi-atom clusters have been found to exhibit physical properties beyond those available from the standard elements in the periodic table; classification of the properties of such clusters effectively enables expansion of the periodic table to a third dimension. Using clusters as superatomic building blocks for hierarchically assembled materials allows these properties to be incorporated into designer materials with tailored properties. Cluster-assembled materials are currently being explored and methods developed to control their design and function. Here, we discuss examples of building block syntheses, assembly strategies, and property control achieved to date.

Assembling crystals from clusters

Abstract: It is shown that the stability of a cluster can be substantially enhanced by changing its size and/or composition so as to take advantage of the electronic shell filling as well as close atomic packing. The interaction between two such clusters is found to be weak and can form the basis for synthesizing a new class of cluster-assembled crystals with uncommong properties.

Formation of Al13I-: evidence for the superhalogen character of Al13.

Abstract: Al13- is a cluster known for the pronounced stability that arises from coincident closures of its geometric and electronic shells. We present experimental evidence for a very stable cluster corresponding to Al13I-. Ab initio calculations show that the cluster features a structurally unperturbed Al13- core and a region of high charge density on the aluminum vertex opposite from the iodine atom. This ionically bound magic cluster can be understood by considering that Al13 has an electronic structure reminiscent of a halogen atom. Comparisons to polyhalides provide a sound explanation for our chemical observations.

Clusters, Superatoms, and Building Blocks of New Materials†

Abstract: The physical and chemical properties of cluster systems at the subnano and nanoscale are often found to differ from those of the bulk and display a unique dependence on size, geometry, and composition. Indeed, most interesting are systems which have properties that vary discontinuously with the number of atoms and composition, rather than scale linearly with size. This realm of cluster science where “one atom makes a difference” is undergoing an explosive growth in activity, and as a result of extensive collaborative activities through theory at VCU and experiment at PSU, our groups are recognized as pioneers in this area in which we have been active for many years. Herein we provide an overview of the field with primary focus on our joint undertakings which have spawned the superatom concept, giving rise to a 3-D periodic table of cluster elements and the prospect of using these as building blocks of new nanoscale materials with tailored properties.

Physics and Chemistry of Finite Systems: From Clusters to Crystals

Abstract: Volume 1: atomic structure stability and evolution dynamics electronic structure magnetism. Volume 2: electrical and optical properties cluster reactions and cluster-support interactions cluster assemblies materials involving carbon.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Molecular dynamics study of melting and freezing of small Lennard-Jones clusters

Abstract: The properties of small clusters of Lennard-Jones atoms were studied by using molecular dynamics simulations. Clusters containing from 13 to 147 atoms were found to undergo a transition, analogous to a melting transition for bulk materials, from a low-energy solidlike structure at low temperatures to a set of higher energy liquidlike structures at high temperatures. The transition creates noticeable features in plots of the equilibrium energy of clusters as a function of temperature, but the shapes of the curves depend on the size of the cluster and on whether a canonical ensemble or microcanonical ensemble is used for calculating the properties. The nonequilibrium energy as a function of temperature on heating or cooling at a finite rate can differ significantly from the equilibrium results. Coexistence among the minimum-energy structure, high-energy liquidlike structures, and typically one or more intermediate structures was observed over a range of temperatures. Results from potential energy minimization of fee and icosahedral structures of various sizes indicate that a Lennard-Jones cluster must contain at least 5000 atoms before the fee structure becomes more stable than the structure of the Mackay icosahedra.

Atomically Precise Colloidal Metal Nanoclusters and Nanoparticles: Fundamentals and Opportunities

Abstract: Colloidal nanoparticles are being intensely pursued in current nanoscience research. Nanochemists are often frustrated by the well-known fact that no two nanoparticles are the same, which precludes the deep understanding of many fundamental properties of colloidal nanoparticles in which the total structures (core plus surface) must be known. Therefore, controlling nanoparticles with atomic precision and solving their total structures have long been major dreams for nanochemists. Recently, these goals are partially fulfilled in the case of gold nanoparticles, at least in the ultrasmall size regime (1–3 nm in diameter, often called nanoclusters). This review summarizes the major progress in the field, including the principles that permit atomically precise synthesis, new types of atomic structures, and unique physical and chemical properties of atomically precise nanoparticles, as well as exciting opportunities for nanochemists to understand very fundamental science of colloidal nanoparticles (such as the s...

Directed Self-Assembly of Nanoparticles

Abstract: Within the field of nanotechnology, nanoparticles are one of the most prominent and promising candidates for technological applications. Self-assembly of nanoparticles has been identified as an important process where the building blocks spontaneously organize into ordered structures by thermodynamic and other constraints. However, in order to successfully exploit nanoparticle self-assembly in technological applications and to ensure efficient scale-up, a high level of direction and control is required. The present review critically investigates to what extent self-assembly can be directed, enhanced, or controlled by either changing the energy or entropy landscapes, using templates or applying external fields.

Size matters: why nanomaterials are different

Abstract: Gold is known as a shiny, yellow noble metal that does not tarnish, has a face centred cubic structure, is non-magnetic and melts at 1336 K. However, a small sample of the same gold is quite different, providing it is tiny enough: 10 nm particles absorb green light and thus appear red. The meltingtemperature decreases dramatically as the size goes down. Moreover, gold ceases to be noble, and 2–3 nm nanoparticles are excellent catalysts which also exhibit considerable magnetism. At this size they are still metallic, but smaller ones turn into insulators. Their equilibrium structure changes to icosahedral symmetry, or they are even hollow or planar, depending on size. The present tutorial review intends to explain the origin of this special behaviour of nanomaterials.