HPC applications heavily rely on Message Passing Interface (MPI) and SHMEM programming models to develop distributed memory parallel applications. This paper describes a set of new features and optimizations that have been introduced in Cray MPT software libraries to optimize the performance of scientific parallel applications on modern Cray XC series supercomputers. For Cray XC systems based o...

The cystine/glutamate exchanger (system xc (-)) mediates the transport of cystine into the cell in exchange for glutamate. By releasing glutamate, system xc (-) can potentially cause excitotoxicity. However, through providing cystine to the cell, it regulates the levels of cellular glutathione (GSH), the main endogenous intracellular antioxidant, and may protect cells against oxidative stress. ...

We present a detailed study of different exchange-correlation (xc) functionals in describing the dynamical properties of finite systems. For that purpose, we calculated the static polarizabilities, ionization potentials and optical absorption spectrum of four small clusters, Na2, Na4, SiH4 and Si2H6, using a real-space, real-time technique. The computed static polarizabilities and ionization po...

We have investigated the suitability of Time-Dependent Density Functional Theory (TD-DFT) to describe vertical low-energy excitations in naked and hydrated titanium dioxide nanoparticles. Specifically, we compared TD-DFT results obtained using different exchange-correlation (XC) potentials with those calculated using Equation-of-Motion Coupled Cluster (EOM-CC) quantum chemistry methods. We demo...

Second order Møller-Plesset perturbation theory at the complete basis set limit and diffusion quantum Monte Carlo are used to examine several low energy isomers of the water hexamer. Both approaches predict the so-called prism to be the lowest energy isomer, followed by cage, book, and cyclic isomers. The energies of the four isomers are very similar, all being within 10-15 meV/H(2)O. These ref...

Multiwalled carbon nanotube-supported Pt (Pt/MWNT) nanocomposites were prepared by both the aqueous solution reduction of a Pt salt (HCHO reduction) and the reduction of a Pt ion salt in ethylene glycol solution. For comparison, a Pt/XC-72 nanocomposite was also prepared by the EG method. The Pt/MWNT catalyst prepared by the EG method has a high and homogeneous dispersion of spherical Pt metal ...

We apply the frozen density embedding method, using a full relaxation of embedded densities through a freeze-and-thaw procedure, to study the electronic structure of several benchmark ground-state charge-transfer complexes, in order to assess the merits and limitations of the approach for this class of systems. The calculations are performed using both semilocal and hybrid exchange-correlation ...

We describe a simple model for calculating the zero-temperature superfluid density of Zn-doped YBa2Cu3O7−δ as a function of the fraction x of in-plane Cu atoms which are replaced by Zn. The basis of the calculation is a “Swiss cheese” picture of a single CuO2 layer, in which a substitutional Zn impurity creates a normal region of area πξ2 ab around it as originally suggested by Nachumi et al. H...

The concept of orbitaland eigenvalue-dependent exchangeŽ . correlation xc energy functionals is reviewed. We show how such functionals can be derived in a systematic fashion via a perturbation expansion, utilizing the Kohn]Sham system as a noninteracting reference system. We demonstrate that the second-order contribution to this expansion of the xc-energy functional includes the leading term of...

Modern compute architectures such as the Intel Many Integrated Core (MIC) and the NVIDIA GPUs are shaping the landscape of supercomputing systems. Current generation interconnect technologies, such as the Cray Aries, are further fueling the design and development of extreme scale systems. Message Passing Interface (MPI) and SHMEM programming models offer high performance, portability and high p...