Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 21 for “"correlation energy"”.
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Assessment of the scaled Perdew-Zunger self-interaction correction applied to three levels of density functional approximations
… the many-electron problem for the ground state energy and density by solving the self-consistent one-electron Schr\"{o}dinger equations. KS-DFT would be an exact theory if we could find the precise form of exchange-correlation energy $(E_{xc})$. However, this would not be computationally …
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Quantum Monte Carlo methods for molecular systems: New developments and applications
… approaches, (ii) determine the impact of correlation energy on a variety of systems in which correlation is important, (iii) investigate new silicon clusters which may generate unique materials, (iv) determine the most stable C$\sb{10}$ and C$\sb{20}$ clusters, (v) achieve kcal/mol …
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Quantum Monte Carlo methods for molecular systems: New developments and applications
… approaches, (ii) determine the impact of correlation energy on a variety of systems in which correlation is important, (iii) investigate new silicon clusters which may generate unique materials, (iv) determine the most stable C10 and C2o clusters, (v) achieve kcal/mol accuracy for …
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Backflow and pairing wave function for quantum Monte Carlo methods
… retrieves an additional 50% of the remaining correlation energy at the variational Monte Carlo level, and 30% at the diffusion Monte Carlo level; the number of parameters required to achieve a given fraction of the correlation energy does not appear to increase with system size. The expense …
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Quantum Embedding Methods for the Accurate Ground and Excited Electronic Structure of Large Molecular Systems
… allows BE to converged to at least 99\% of the correlation energy in basis sets up to cc-pVDZ. For the troublesome cases involving more diffuse and polarization effects, pair natural orbitals (PNOs) were reformulated for the embedding framework and BE with PNOs, PNO-BE, demonstrated a faster …
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Construction of first-principles density functional approximations and their applications to materials
… requires approximation of one term in its total energy expression: the exchange-correlation energy. This work elucidates systematic methods for constructing approximations to the exchange-correlation energy solely from first-principles physics. We review the constraints that can be built into …
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Multi-Reference Pseudo-Random Phase-Encoded Joint Transfrom Correlation
… images and at the same time eliminate false correlation peaks through power spectrum dispersion. A theoretical model of the implemented JTC is mathematically expressed and explained in this thesis. Basic performance criteria, PSR (peak to side lobe ratio) and PCE (peak to correlation energy), …
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Approximate Spin Extended Hartree-Fock theory
… means for obtaining a significant amount of correlation energy in molecular calculations. Moreover, when the Generalized Valence Bond form of the ASEHF wavefunction is employed, a particularly useful description of the molecule is obtained. Specifically, the success or failure of the …
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Real time density functional simulations of quantum scale conductance
… exchange included in the approximate exchange-correlation energy functional. This functional dependence is further illustrated when we demonstrate that the conductance gap of a device imperfectly coupled to wires varies based upon the non-local exchange and correlation. We also study the …
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A quantum Monte Carlo study of the two-dimensional electron gas
… With introduction of backflow and three-body correlations, we find significant improvements in both variational and fixed-node energies over the Slater-Jastrow results which consider only two-body correlations. It is found that the backflow effect is dominant over the three-body effect at high …
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Improved wave functions for quantum Monte Carlo
… atoms and singly-positive ions. Over 98% of the correlation energy is retrieved at the VMC level and over 99% at the DMC level for all the atoms and ions. Their first ionization potentials are calculated within chemical accuracy. Scalar relativistic corrections to the energies, mass-polarization …
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Explicitly Correlated Methods for Large Molecular Systems
… system as well as very slow convergence of the correlation energy with respect to the basis set size. Thus these methods are limited to small systems of up to a dozen atoms. The first of these issues can be efficiently resolved by exploiting the local nature of electron correlation effects while …
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Correcting the Self-Interaction Error of Approximate Density Functionals
… approximations (DFAs) for the exchange-correlation energy suffer from self-interaction error (SIE), which is believed to be the cause of many of the failures of these approximations, such as poor description of charge transfer and transition states of chemical reactions. The standard …
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Characterizing Non-Covalent Interactions And Peptide Bond Formation With Electronic Structure Theory
… dimers and the importance of higher-order correlation corrections. Chapter 7 analyzes the low-energy dimers of the homogeneous and heterogeneous dimers of formaldehyde and thioformaldehyde as well as the associated vibrational frequencies. This work highlights some significant deficiencies …
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Exchange-Correlation Kernels Within Time-Dependent Density Functional Theory For Ground-State and Excited-State Properties
The exact exchange-correlation kernel is a functional derivative of the exact time-dependent exchange-correlation (XC) potential with respect to the time-dependent density, evaluated at the ground-state density. As the XC potential is not known, the exact kernel is also unavailable. Therefore, it …
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Studies of and methods for electronic properties of large chemical systems
… the original DMET equations to account for correlation in the bath via an antisymmetrized geminal power (AGP) wave function. The resulting formalism has a number of advantages. First, it allows one to properly treat the weak correlation limit of independent pairs, which DMET is unable to do …
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Orbital Polarization in Relativistic Density Functional Theory
… In the framework of DFT, usually the total energy is decomposed into kinetic energy, Coulomb energy, and a term called the exchange-correlation energy. Taking into account the relativistic kinetic energy leads to direct and indirect relativistic effects on the electronic structure of a …
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Importance of Self-Interaction Correction in Hydrogen-Bonded Water Clusters and Water-Ion Clusters
… of the self-Hartree and the self exchange correlation energy, has long been identified as a major limitation of practical density functional approximations. We develop and test the performance of different self-interaction corrected functionals in accurately predicting a wide range of …
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Theoretical and Computational Aspects of the Optimized Effective Potential Approach within Density Functional Theory
… of suitable approximations to the exchange-correlation energy functional. Use of functional approximations depending explicitly upon the density alone appear unable to address all aspects of many-body interactions, such as the fundamental constraint that the ground state energy is a …
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Advancements in Monte Carlo many body methods
… the operational cost to compute the k-order energy correction with many-body perturbation theory (MBPT) is O (n k+3 ), with n being proportional to the molecular size. Additionally, many-body methods are typically cast into complex series of dense matrix-matrix multiplications, which is …
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