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11.
Shao Y Molnar LF Jung Y Kussmann J Ochsenfeld C Brown ST Gilbert AT Slipchenko LV Levchenko SV O'Neill DP DiStasio RA Lochan RC Wang T Beran GJ Besley NA Herbert JM Lin CY Van Voorhis T Chien SH Sodt A Steele RP Rassolov VA Maslen PE Korambath PP Adamson RD Austin B Baker J Byrd EF Dachsel H Doerksen RJ Dreuw A Dunietz BD Dutoi AD Furlani TR Gwaltney SR Heyden A Hirata S Hsu CP Kedziora G Khalliulin RZ Klunzinger P Lee AM Lee MS Liang W Lotan I Nair N Peters B Proynov EI Pieniazek PA Rhee YM 《Physical chemistry chemical physics : PCCP》2006,8(27):3172-3191
Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package, together with illustrative timings and applications. Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces. 相似文献
12.
Niederdraenk F Seufert K Stahl A Bhalerao-Panajkar RS Marathe S Kulkarni SK Neder RB Kumpf C 《Physical chemistry chemical physics : PCCP》2011,13(2):498-505
The detailed structural characterization of nanoparticles is a very important issue since it enables a precise understanding of their electronic, optical and magnetic properties. Here we introduce a new method for modeling the structure of very small particles by means of powder X-ray diffraction. Using thioglycerol-capped ZnO nanoparticles with a diameter of less than 3 nm as an example we demonstrate that our ensemble modeling method is superior to standard XRD methods like, e.g., Rietveld refinement. Besides fundamental properties (size, anisotropic shape and atomic structure) more sophisticated properties like imperfections in the lattice, a size distribution as well as strain and relaxation effects in the particles and-in particular-at their surface (surface relaxation effects) can be obtained. Ensemble properties, i.e., distributions of the particle size and other properties, can also be investigated which makes this method superior to imaging techniques like (high resolution) transmission electron microscopy or atomic force microscopy, in particular for very small nanoparticles. For the particles under study an excellent agreement of calculated and experimental X-ray diffraction patterns could be obtained with an ensemble of anisotropic polyhedral particles of three dominant sizes, wurtzite structure and a significant relaxation of Zn atoms close to the surface. 相似文献
13.
Gupta R Sheth DM Boone TK Sevilla AB Fréchette J 《Langmuir : the ACS journal of surfaces and colloids》2011,27(24):14923-14929
Pinning of the triple contact line adversely affects electrowetting on dielectric. Electrowetting response of substrates with contact angle hysteresis ranging from 1° to 30° has been characterized, and the results are interpreted within the framework of electromechanics corrected for pinning. The relationship between contact angle hysteresis, threshold potential for liquid actuation, and electrowetting hysteresis is quantified. Our results demonstrate that a modified electrowetting equation, based on balance of forces (including the pinning forces) acting on the triple contact line and on the drop, describes the electrowetting response of substrates with significant contact angle hysteresis. Finally, the surface properties of PDMS Sylgard 184 were found to be influenced by the electric field. 相似文献
14.
Rohini Mani Michael Fischer Joby E. Joy J. Gopalakrishnan Martin Jansen 《Solid State Sciences》2009,11(1):189-194
We describe an exploratory investigation of the structure and electronic properties of new ruthenium(IV) pyrochlore oxides and their manganese-substituted derivatives. Our investigations have revealed several, hitherto unreported, electronic ground states for these materials: a metallic and Pauli paramagnetic state for BiPbRu2O6.5 that turns into a semiconducting ferromagnetic spin-glass state at 50 K for BiPbRuMnO6.5; a metallic state that likely shows a charge density wave (CDW) instability at 50–225 K for Bi1.50Zn0.50Ru2O6.75 that is suppressed by manganese substitution in Bi1.50Zn0.50Ru1.75Mn0.25O6.50; and a metallic ferromagnetic spin-glass like state for Pb2Ru1.75Mn0.25O6.15. The results indeed affirm the richness of the electronic properties of ruthenium-based metal oxides. 相似文献
15.
Rohini S. Bhalerao-Panajkar Mandar M. Shirolkar Raja Das Pankaj Poddar 《Solid State Communications》2011,151(1):55-60
Cupric oxide nanoparticles of ∼8-10 nm width and 40-45 nm length self assembled as large particles ∼1-1.5 μm have been investigated, in the 10-325 K temperature range, using magnetic and dielectric measurements. In magnetic measurements a single broad peak at ∼230 K in a zero field cooled sample has been observed. Coercivity, in magnetization measurements at 10 K, suggests that the nanoparticles are core-shell type particles with an antiferromagnetic core and a ferromagnetic shell. Dielectric measurements, at various frequencies from 3.7 Hz to 949 kHz, exhibit a sharp peak at 284 K followed by weak anomalies around 213 and 230 K. 相似文献
16.
Consider a system of particles evolving as independent and identically distributed (i.i.d.) random walks. Initial fluctuations
in the particle density get translated over time with velocity [(v)\vec]\vec{v}, the common mean velocity of the random walks. Consider a box centered around an observer who starts at the origin and moves
with constant velocity [(v)\vec]\vec{v}. To observe interesting fluctuations beyond the translation of initial density fluctuations, we measure the net flux of particles
over time into this moving box. We call this the “box-current” process. 相似文献
17.
18.
Benighaus T DiStasio RA Lochan RC Chai JD Head-Gordon M 《The journal of physical chemistry. A》2008,112(12):2702-2712
The recently proposed new family of "double-hybrid" density functionals [Grimme, S. J. Chem. Phys. 2006, 124, 34108] replaces a fraction of the semi-local correlation energy by a non-local correlation energy expression that employs the Kohn-Sham orbitals in second-order many-body perturbation theory. These functionals have provided results of high accuracy over a wide range of properties but fail to accurately describe long-range van der Waals interactions. In this work, a distance-dependent scaling factor for the non-local correlation energy is introduced to address this problem, and two new double-hybrid density functionals are proposed. The new functionals are optimized with the finite cc-pVTZ basis on training sets of atomization energies and intermolecular interaction energies. They are compared against (scaled) second-order M?ller-Plesset perturbation theories and popular density functionals including the hybrid-GGA functional B3-LYP and the first double-hybrid functional (B2-PLYP). Tests are performed on an extensive set including reaction energies, barrier heights, weakly interacting complexes, transition-metal systems, molecular geometries, and harmonic vibrational frequencies. Within the cc-pVTZ atomic orbital basis, we have demonstrated the ability to find a parametrization scheme which is simultaneously able to describe thermochemistry and weakly bound systems with a satisfactory degree of accuracy. 相似文献
19.
Molecular hydrogen is known to form stable, "nonclassical" sigma complexes with transition metal centers that are stabilized by donor-acceptor interactions and electrostatics. In this computational study, we establish that strong H2 sorption sites can be obtained in metal-organic frameworks by incorporating open transition metal sites on the organic linkers. Using density functional theory and energy decomposition analysis, we investigate the nature and characteristics of the H2 interaction with models of exposed open metal binding sites {half-sandwich piano-stool shaped complexes of the form (Arene)ML(3- n)(H2)n [M=Cr, Mo, V(-), Mn(+); Arene = C6H5X (X=H, F, Cl, OCH3, NH2, CH3, CF3) or C6H3Y2X (Y=COOH, X=CF3, Cl; L=CO; n=1-3]}. The metal-H2 bond dissociation energy of the studied complexes is calculated to be between 48 and 84 kJ/mol, based on the introduction of arene substituents, changes to the metal core, and of charge-balancing ligands. Thus, design of the binding site controls the H2 binding affinity and could be potentially used to control the magnitude of the H2 interaction energy to achieve reversible sorption characteristics at ambient conditions. Energy decomposition analysis illuminates both the possibilities and present challenges associated with rational materials design. 相似文献
20.
Satav SS Karmalkar RN Kulkarni MG Mulpuri N Sastry GN 《Journal of the American Chemical Society》2006,128(24):7752-7753
Ethylene glycol dimethacrylate (EGDMA) and ethylene glycol methacrylate 4-vinyl benzoate (EGMAVB) were shown to form 1:1 inclusion complexes with cyclodextrin and were characterized by instrumental techniques. Computational analysis showed that the bent conformation of the included divinyl monomer was more stable than its linear conformation. Complexation of the divinyl monomer with the first CD molecule offered substantial stabilization than with the second CD molecule. The vinyl group included in the CD cavity did not participate in polymerization. As a result, solvent soluble, linear polymers with pendant vinyl unsaturation per repeat unit were obtained. This was unequivocally established by the polymerization of a complex comprising CD and EGMAVB. The unreacted vinyl group can be polymerized in the subsequent step to yield cross-linked products. 相似文献