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Brabec J.,Computational Research DivisionLawrence Berkeley National LaboratoryBerkeley | Yang C.,Computational Research DivisionLawrence Berkeley National LaboratoryBerkeley | Epifanovsky E.,University of Southern California | Krylov A.I.,University of Southern California | Ng E.,Computational Research DivisionLawrence Berkeley National LaboratoryBerkeley
Journal of Computational Chemistry | Year: 2016

We present an algorithm for reducing the computational work involved in coupled-cluster (CC) calculations by sparsifying the amplitude correction within a CC amplitude update procedure. We provide a theoretical justification for this approach, which is based on the convergence theory of inexact Newton iterations. We demonstrate by numerical examples that, in the simplest case of the CCD equations, we can sparsify the amplitude correction by setting, on average, roughly 90% nonzero elements to zeros without a major effect on the convergence of the inexact Newton iterations. © 2016 Wiley Periodicals, Inc. Source


Zuev D.,University of Southern California | Vecharynski E.,Computational Research DivisionLawrence Berkeley National LaboratoryBerkeley | Yang C.,Computational Research DivisionLawrence Berkeley National LaboratoryBerkeley | Orms N.,University of Southern California | Krylov A.I.,University of Southern California
Journal of Computational Chemistry | Year: 2014

New algorithms for iterative diagonalization procedures that solve for a small set of eigen-states of a large matrix are described. The performance of the algorithms is illustrated by calculations of low and high-lying ionized and electronically excited states using equation-of-motion coupled-cluster methods with single and double substitutions (EOM-IP-CCSD and EOM-EE-CCSD). We present two algorithms suitable for calculating excited states that are close to a specified energy shift (interior eigenvalues). One solver is based on the Davidson algorithm, a diagonalization procedure commonly used in quantum-chemical calculations. The second is a recently developed solver, called the “Generalized Preconditioned Locally Harmonic Residual (GPLHR) method.“ We also present a modification of the Davidson procedure that allows one to solve for a specific transition. The details of the algorithms, their computational scaling, and memory requirements are described. The new algorithms are implemented within the EOM-CC suite of methods in the Q-Chem electronic structure program. © 2014 Wiley Periodicals, Inc. Source

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