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Author

Stephen Bell

Other affiliations: University of Oxford
Bio: Stephen Bell is an academic researcher from University of Dundee. The author has contributed to research in topics: Ab initio & Ab initio quantum chemistry methods. The author has an hindex of 17, co-authored 56 publications receiving 922 citations. Previous affiliations of Stephen Bell include University of Oxford.


Papers
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Journal ArticleDOI
TL;DR: In this article, a method for locating saddle points on multidimensional surfaces by combining aspects of the conjugate gradients method and the quasi-Newton minimization method is described with modifications to make it more robust.
Abstract: A previously reported method for locating saddle points on multidimensional surfaces by a combination of aspects of the conjugate gradients method and the quasi‐Newton minimization method is now described with modifications to make it more robust. A number of model potentials from the literature and some ab initio molecular potential energy surfaces are used for test and comparison purposes.

226 citations

Journal ArticleDOI
TL;DR: A direct method is described for locating saddle points on multidimensional surfaces that combines aspects of the conjugate gradient method and the quasi-Newton minimization method.

51 citations

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TL;DR: In this paper, a wide range of basis sets and ab initio theoretical methods up to MP4 have been used in order to predict the cis-gauche conformational energy difference.

44 citations

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TL;DR: In this article, a new emission system of CS has been observed in the vacuum and near ultraviolet produced by a microwave discharge in carbon disulphide. The system arises from the transition A ǫ 1 Σ + -X 1 Á +.

40 citations

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TL;DR: In this paper, the rotational constants for the excited state are S ‘ = 1.8755, B ‘ 0.4042, C ‘= 0.3378 cm −1 by the plausible assumption that the important changes in the molecule are in the C=0 bond length, the OCO angle, and the nonplanarity due to the formyl hydrogen.

37 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a modified conjugate gradient algorithm for geometry optimization is presented for use with ab initio MO methods, where the second derivative matrix rather than its inverse is updated employing the gradients.
Abstract: A modified conjugate gradient algorithm for geometry optimization is outlined for use with ab initioMO methods. Since the computation time for analytical energy gradients is approximately the same as for the energy, the optimization algorithm evaluates and utilizes the gradients each time the energy is computed. The second derivative matrix, rather than its inverse, is updated employing the gradients. At each step, a one-dimensional minimization using a quartic polynomial is carried out, followed by an n-dimensional search using the second derivative matrix. By suitably controlling the number of negative eigenvalues of the second derivative matrix, the algorithm can also be used to locate transition structures. Representative timing data for optimizations of equilibrium geometries and transition structures are reported for ab initioSCF–MO calculations.

3,373 citations

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TL;DR: In this paper, a redundant internal coordinate system for molecular geometries is constructed from all bonds, all valence angles between bonded atoms, and all dihedral angles between pairs of atoms.
Abstract: A redundant internal coordinate system for optimizing molecular geometries is constructed from all bonds, all valence angles between bonded atoms, and all dihedral angles between bonded atoms. Redundancies are removed by using the generalized inverse of the G matrix; constraints can be added by using an appropriate projector. For minimizations, redundant internal coordinates provide substantial improvements in optimization efficiency over Cartesian and nonredundant internal coordinates, especially for flexible and polycyclic systems. Transition structure searches are also improved when redundant coordinates are used and when the initial steps are guided by the quadratic synchronous transit approach. © 1996 by John Wiley & Sons, Inc.

2,577 citations

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TL;DR: In this paper, a linear synchronous transit or quadratic synchronous transmisson approach is used to get closer to the quad-ratic region of the transition state and then quasi-newton or eigenvector following methods are used to complete the optimization.
Abstract: A linear synchronous transit or quadratic synchronous transit approach is used to get closer to the quadratic region of the transition state and then quasi-newton or eigenvector following methods are used to complete the optimization. With an empirical estimate of the hessian, these methods converge efficiently for a variety of transition states from a range of starting structures.

1,849 citations

Journal ArticleDOI
TL;DR: In this article, an algorithm for locating transition states designed for use in the ab initio program package GAUSSIAN 82 is presented, which can locate transition states even if started in the wrong region of the energy surface.
Abstract: An algorithm for locating transition states designed for use in the ab initio program package GAUSSIAN 82 is presented. It is capable of locating transition states even if started in the wrong region of the energy surface, and, by incorporating the ideas on hessian mode following due to Cerjan and Miller, can locate transition states for alternative rearrangement/dissociation reactions from the same initial starting point. It can also be used to locate minima.

1,331 citations

Journal ArticleDOI
TL;DR: A generalized synchronous transit method for locating transition state structures or first-order saddle points was proposed in this article, which is based on the established scheme of combining the linear or quadratic synchronized transit method with conjugate gradient refinements but generalized to deal with molecular and periodic systems in a seamless manner.

998 citations