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Search Results: 1 - 10 of 325854 matches for " S. Olsen "
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Observations of Au, Ag, Zn and Pb in crude oils from basins in geographic proximity to ore deposits
S. D. Olsen
Chinese Science Bulletin , 1998, DOI: 10.1007/BF02891533
Analysis of alpha backgrounds in the DEAP-1 detector
Kevin S. Olsen
Physics , 2009,
Abstract: DEAP-1 is a 7 kg liquid argon dark matter detector used to prototype the tonne scale DEAP-3600 detector at SNOLAB.We present an analysis of the alpha particle backgrounds in DEAP-1 and isolate the radiations from various 222Rn daughters at various locations within the detector. The backgrounds will be removed by event position reconstruction and strict controls of material purity.
Relationship between13C/12C isotope ratio and the V/(V+Ni) of petroleum
S. D. Olsen,D. Karlsen
Chinese Science Bulletin , 1998, DOI: 10.1007/BF02891534
Accurate Ground State Energies of Solids and Molecules from Time Dependent Density Functional Theory
Thomas Olsen,Kristian S. Thygesen
Physics , 2014, DOI: 10.1103/PhysRevLett.112.203001
Abstract: We demonstrate that ground state energies approaching chemical accuracy can be obtained by combining the adiabatic connection fluctuation-dissipation theorem (ACFDT) with time-dependent density functional theory (TDDFT). The key ingredient is a renormalization scheme, which eliminates the divergence of the correlation hole characteristic of any local kernel. This new class of renormalized kernels gives a significantly better description of the short-range correlations in covalent bonds compared to the random phase approximation (RPA) and yields a four fold improvement of RPA binding energies in both molecules and solids. We also consider examples of barrier heights in chemical reactions, molecular adsorption and graphene interacting with metal surfaces, which are three examples where RPA has been successful. In these cases, the renormalized kernel provides results that are of equal quality or even slightly better than RPA, with a similar computational cost.
Static correlation beyond the random phase approximation: Dissociating H2 with the Bethe-Salpeter equation and time-dependent GW
Thomas Olsen,Kristian S. Thygesen
Physics , 2013, DOI: 10.1063/1.4871875
Abstract: We investigate various approximations to the correlation energy of a H$_2$ molecule in the dissociation limit, where the ground state is poorly described by a single Slater determinant. The correlation energies are derived from the density response function and it is shown that response functions derived from Hedin's equations (Random Phase Approximation (RPA), Time-dependent Hartree-Fock (TDHF), Bethe-Salpeter equation (BSE), and Time-Dependent GW (TDGW)) all reproduce the correct dissociation limit. We also show that the BSE improves the correlation energies obtained within RPA and TDHF significantly for intermediate binding distances. A Hubbard model for the dimer allow us to obtain exact analytical results for the various approximations, which is readily compared with the exact diagonalization of the model. Moreover, the model is shown to reproduce all the qualitative results from the \textit{ab initio} calculations and confirms that BSE greatly improves the RPA and TDHF results despite the fact that the BSE excitation spectrum breaks down in the dissociation limit. In contrast, Second Order Screened Exchange (SOSEX) gives a poor description of the dissociation limit, which can be attributed to the fact that it cannot be derived from an irreducible response function.
Beyond the random phase approximation: Improved description of short range correlation by a renormalized adiabatic local density approximation
Thomas Olsen,Kristian S. Thygesen
Physics , 2013, DOI: 10.1103/PhysRevB.88.115131
Abstract: We assess the performance of a recently proposed renormalized adiabatic local density approximation (rALDA) for \textit{ab initio} calculations of electronic correlation energies in solids and molecules. The method is an extension of the random phase approximation (RPA) derived from time-dependent density functional theory and the adiabatic connection fluctuation-dissipation theorem and contains no fitted parameters. The new kernel is shown to preserve the accurate description of dispersive interactions from RPA while significantly improving the description of short range correlation in molecules, insulators, and metals. For molecular atomization energies the rALDA is a factor of 7(4) better than RPA(PBE) when compared to experiments, and a factor of 3(1.5) better than RPA(PBE) for cohesive energies of solids. For transition metals the inclusion of full shell semi-core states is found to be crucial for both RPA and rALDA calculations and can improve the cohesive energies by up to 0.4 eV. Finally we discuss straightforward generalizations of the method, which might improve results even further.
The random phase approximation applied to solids, molecules, and graphene-metal interfaces: From weak to strong binding regimes
Thomas Olsen,Kristian S. Thygesen
Physics , 2012, DOI: 10.1103/PhysRevB.87.075111
Abstract: The random phase approximation (RPA) is attracting renewed interest as a universal and accurate method for first-principles total energy calculations. The RPA naturally accounts for long-range dispersive forces without compromising accuracy for short range interactions making the RPA superior to semi-local and hybrid functionals in systems dominated by weak van der Waals or mixed covalent-dispersive interactions. In this work we present plane wave-based RPA calculations for a broad collection of systems with bond types ranging from strong covalent to van der Waals. Our main result is the RPA potential energy surfaces of graphene on the Cu(111), Ni(111), Co(0001), Pd(111), Pt(111), Ag(111), Au(111), and Al(111) metal surfaces, which represent archetypical examples of metal-organic interfaces. Comparison with semi-local density approximations and a non-local van der Waals functional show that only the RPA captures both the weak covalent and dispersive forces which are equally important for these systems. We benchmark our implementation in the GPAW electronic structure code by calculating cohesive energies of graphite and a range of covalently bonded solids and molecules as well as the dissociation curves of H2 and H2+. These results show that RPA with orbitals from the local density approximation suffers from delocalization errors and systematically underestimates covalent bond energies yielding similar or lower accuracy than the Perdew-Burke-Ernzerhof (PBE) functional for molecules and solids, respectively.
Extending the random-phase approximation for electronic correlation energies: The renormalized adiabatic local density approximation
Thomas Olsen,Kristian S. Thygesen
Physics , 2012, DOI: 10.1103/PhysRevB.86.081103
Abstract: The adiabatic connection fluctuation-dissipation theorem with the random phase approximation (RPA) has recently been applied with success to obtain correlation energies of a variety of chemical and solid state systems. The main merit of this approach is the improved description of dispersive forces while chemical bond strengths and absolute correlation energies are systematically underestimated. In this work we extend the RPA by including a parameter-free renormalized version of the adiabatic local density (ALDA) exchange-correlation kernel. The renormalization consists of a (local) truncation of the ALDA kernel for wave vectors $q>2k_F$, which is found to yield excellent results for the homogeneous electron gas. In addition, the kernel significantly improves both the absolute correlation energies and atomization energies of small molecules over RPA and ALDA. The renormalization can be straightforwardly applied to other adiabatic local kernels.
Rapidly Progressive Lung Cysts and Pleural Effusion: A Case Report
Diana Olsen,Charlene Molloy,P. S. Sriram
Case Reports in Pulmonology , 2011, DOI: 10.1155/2011/790274
Abstract: Angiosarcoma is a rare but highly malignant tumor arising from vascular endothelial cells. Angiosarcoma commonly arises from the heart, liver, breast, and skin including the scalp. Angiosarcoma metastasizing to the lungs can present as either pneumothorax, hemothorax, or pleural effusions. They can rarely present as rapidly enlarging thin-walled pulmonary cysts. A review of the literature is included.
Optimal Co-Generation in an Integrated Kraft Mill
S. Suh,T.O. Olsen
Modeling, Identification and Control , 1982, DOI: 10.4173/mic.1982.1.2
Abstract: An optimal control system designed to minimize the consumption of high pressure steam (and thus minimizing energy costs) while meeting the paper mill's demand for process steam and electric power is developed. An installation example is described and system performance and benefits are discussed. It should be noted that the theories developed in this paper can be readily extended to the design of an optimal control system which maximizes the electric generation under the given inlet steam flow.
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