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Showing 1 to 20 of 54 for “"Coupled Cluster"”.
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Stochastic Approaches to Coupled Cluster Theory
… of various new approaches to solving the Coupled Cluster (CC) equations through Monte Carlo (MC) integration. Firstly, exact importance sampling of the CC wavefunction to arbitrary order is defined and applied as a modification to the extant unlinked Coupled Cluster Monte Carlo (CCMC) …
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Novel Ansätze for Stochastic Coupled Cluster
… two new types of algorithms in the framework of Coupled Cluster Monte Carlo (CCMC). First, the CCMC paradigm is expanded to multireference coupled cluster (MRCC). The multireference CCMC (mr-CCMC) approach takes advantage of Monte Carlo methods’ ca- pacity to treat any cluster expansion with …
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Local Correlation Approaches and Coupled Cluster Linear Response Theory
… of theoretical models still remain. A coupled cluster singles and doubles (CCSD) calculation, a reliable ab initio method, scales approximately on the order of 𝑂(𝑁⁶), where 𝑁 is a measure of the system size. This unfortunately limits the use of such high-accuracy methods to relatively …
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Light-Front Coupled-Cluster Method In Phi-Four Field Theory
The light-front coupled-cluster (LFCC) method is investigated as an alternative method for determining mass eigenvalues in quantum field theories. Traditional methods create an infinite set of coupled equations, and solutions are then approximated by truncating the system of equations and …
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A multireference coupled-cluster method using a single-reference formalism.
The coupled-cluster (CC) equations including single, double, triple and quadruple excitations (CCSDTQ) are qraphically derived using Feynman diagrams. These equations are programmed and an iterative reduced linear equation method is used to solve these equations. A few points on the potential …
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Towards a Reduced-Scaling Method for Calculating Coupled Cluster Response Properties
… with the size of the system. For example, the coupled cluster singles and doubles method with the perturbative inclusion of triples: the CCSD(T) model, which is considered to be the ``gold standard'' of quantum chemistry scales as 𝑂(N⁷) in its canonical formulation, where $N$ is a measure of …
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Development and Application of Coupled Cluster Ground- and Excited-State Models
… with previous density-functional theory and coupled cluster studies. In addition, the calculated CCSD(T) fundamental frequencies are in excellent agreement with the measured infrared frequencies, thus confirming the monocyclic form of m-benzyne. For tetrafluoro-m-benzyne, however, the …
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Coupled-cluster methods for open-shell molecular and other many-fermion systems
Thesis (Ph. D.)--Michigan State University. Dept. of Chemistry, 2010
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Development and Assessment of Pair Natural Orbitals Coupled Cluster Quadratic Response Properties
… presents a study on the efficacy of LPNO-based coupled cluster (CC) methods for calculating static electric-field properties—including dipole moments, polarizabilities, and first hyperpolarizabilities via numerical differentiation. We find that constructing pair correlation domains independently …
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Coupled-Cluster Methods for Large Molecular Systems Through Massive Parallelism and Reduced-Scaling Approaches
… to small molecular systems. For example, the coupled-cluster singles, doubles, and perturbative triples model (CCSD(T)), which is known as the ``gold standard" of quantum chemistry for its accuracy, usually can treat molecules with 20-30 atoms. To extend the reach of accurate correlated …
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Development of multicomponent coupled-cluster theory and its application to nanoclusters and molecular systems
… the motion of the two particle types is decoupled. While the BO approximation is ubiquitous in computational and theoretical studies, it is not always justifiable. There are two main cases where this approximation is not valid. The first is when nuclear and electronic motion cannot be …
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Investigation of real-time coupled cluster methods for the efficient calculation of optical molecular properties in the time domain
… functional theory, configurational interaction, coupled cluster, etc. Among these, coupled cluster (CC) methods provide high accuracy for systems with strong electron correlation, making RT-CC implementations intriguing. All applications of CC methods face a substantial challenge due to their …
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Accelerating and Converging Stochastic Quantum Chemistry
… versions of quantum chemistry methods such as coupled cluster Monte Carlo (CCMC) or full configuration interaction quantum Monte Carlo (FCIQMC) have made highly accurate energy calculations possible that are not accessible to the corresponding deterministic methods (full configuration …
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Accurate Prediction of Chiroptical Properties
… of optical rotation, finding that at the coupled cluster level of theory they perform the same or better than comparably sized general basis sets that are often used. We have also examined the performance of a perturbational approach to inclusion of explicit solvent molecules in an effort …
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Theoretical Prediction of Electronically Excited States and Vibrational Frequencies of Interstellar and Planetary Radicals, Anions, and Cations
… as well as the cis-HOCO anion. First, open-shell coupled cluster methods of singles and doubles (CCSD) and singles and doubles with triples-inclusion (CC3) are tested on the C₂H and C₄H radicals. The significant double-excitation character, as well as the quartet multiplicity of some states yields …
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Towards an Improved Method for the Prediction of Linear Response Properties of Small Organic Molecules
… of density functional, we would prefer to use coupled cluster theory, a robust and systematically improvable method. However, the high-order polynomial scaling of coupled cluster theory makes it intractable for numerous large calculations, including the conformational averaging required for …
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Ab initio Calculations of Optical Rotation
Coupled cluster (CC) and density functional theory (DFT) are highly regarded as robust quantum chemical methods for accurately predicting a wide variety of properties, such as molecular structures, thermochemical data, vibrational spectra, etc., but there has been little focus on the theoretical …
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An Exploration of Theoretical Spectra
… creation andinterpretation, with a focus on coupled cluster methods and an emphasis on the importance of relativistic effects. Throughout this work the X2C Hamiltonian is utilized to produce the reference wavefunction, including both scalar relativistic effects and spin-orbit coupling …
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The Electronic Excited States of Green Fluorescent Protein Chromophore Models
… functional theory (TDDFT), equation-of motion coupled cluster (EOM-CCSD) and multireference perturbation theory (MRPT). Amongst the low-lying states we identify the optically bright pipi* state of the molecules and examine its properties. We demonstrate that the state is dominated by a single …
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Novel techniques for cold/ultracold molecular collisions
… observed. The near-copropagating beam apparatus coupled with the stimulated emission pumping method and sliced velocity map imaging detection enabled us to measure the state-to-state differential cross sections for inelastic collisions between vibrationally excited NO molecules and Ar at broadly …
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