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Transition state search algorithms, such as the nudged elastic band can fail, if a good initial guess of the transition state structure cannot be provided. The growing string method (GSM) [J. Chem. Phys. 120, 7877 (2004)] eliminates the need for an initial guess of the transition state. While this method only requires knowledge of the reactant and product geometries, it is computationally intensive. To alleviate the bottlenecks in the GSM, several modifications were implemented: Cartesian coordinates were replaced by internal coordinates, the steepest descent method for minimization of orthogonal forces to locate the reaction path was replaced by the conjugate gradient method, and an interpolation scheme was used to estimate the energy and gradient, thereby reducing the calls to the quantum mechanical (QM) code. These modifications were tested to measure the reduction in computational time for four cases of increasing complexity: the Müller–Brown potential energy surface, alanine dipeptide isomerization, H abstraction in methanol oxidation, and C–H bond activation in oxidative carbonylation of toluene to p-toluic acid. These examples show that the modified GSM can achieve two- to threefold speedups (measured in terms of the reduction in actual QM gradients computed) over the original version of the method without compromising accuracy of the geometry and energy of the final transition state. Additional savings in computational effort can be achieved by carrying out the initial search for the minimum energy pathway (MEP) using a lower level of theory (e.g., HF/STO-3G) and then refining the MEP using density functional theory at the B3LYP level with larger basis sets (e.g., 6-31G∗, LANL2DZ). Thus, a general strategy for determining transition state structures is to initiate the modified GSM using a low level of theory with minimal basis sets and then refining the calculation at a higher level of theory with larger basis sets.
We address the task of predicting pose for objects of unannotated object categories from a small seed set of annotated object classes. We present a generalized classifier that can reliably induce pose given a single instance of a novel category. In case of availability of a large collection of novel instances, our approach then jointly reasons over all instances to improve the initial estimates. We empirically validate the various components of our algorithm and quantitatively show that our method produces reliable pose estimates. We also show qualitative results on a diverse set of classes and further demonstrate the applicability of our system for learning shape models of novel object classes.
No abstract is provided for this article.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
In this paper, we introduce a new experimental tool, a real-time programmable, spatial-temporal bifurcation test bed. We present the experimental analysis of an antisymmetric template class. This class produces novel spatial-temporal patterns that exhibit complex dynamics. The character of these propagating patterns depends on the self-feedback and on the sign of the coupling below the self-feedback template element.
A procedure is presented for evaluating building‐code provisions for accidental torsion from analysis of earthquake‐induced motions of nominally symmetric‐plan buildings. This procedure is used to analyze the motions of three buildings recorded during recent California earthquakes. Two alternative approaches to evaluate the code accidental torsion provisions are developed. The first One considers the response histories of base shear and base torque in the building, and the second, the "actual" forces in the structural elements during the earthquake. The results show that base rotational motions cause between 25% and 45% of the total accidental torsion in the buildings. They also demonstrate that the accidental torsional moments specified by the Uniform Building Code are sufficient in representing the torsion in the recorded motions of the three buildings. Further, it is shown that accidental torsion need not be considered in the design of two of the three buildings studied. This observation, however, may not necessarily apply to other structures, such as buildings with torsional vibration periods much longer than their lateral vibration periods.
By means of 29Si NMR spectroscopy, it is established that the distribution of silicate anions in alkaline silicate solutions is a moderate function of base composition. At a fixed SiO2 concentration and silicate ratio, the proportion of Si present in oligomeric and cage-like structures increases in progressing from Li to Cs hydroxide. This trend is ascribed to cation-silicate anion pairing and to a higher selectivity for ion pairing by large silicate anions as cation size increases.
