A Study of Basis Set Effects on Structures and Electronic Structures of Phosphine Oxide and Fluorophosphine Oxide

A variety of basis sets have been used for geometric and electronic structure studies. Electronic effects were measured using integrated spatial electron populations (ISEP). The two largest basis sets used, 6-31G* and DZ+P, give significantly different results. Use of two d-orbital sets (6-31G*[dd]) or decontraction of the 2sp shell on phosphorus has little further effect. d-Orbitals on oxygen are required for consistent electronic structure results, and d-orbitals on fluorine have a small but significant effect. Use of diffuse functions, required for anions, is not recommended with small basis sets on neutral molecules. Large negative charges (≈-1.5) on oxygen are given by all of the larger basis sets by the ISEP procedure and indicate that the PO bond in these compounds is largely semi-polar. The best simple symbolic representation of phosphine oxide is H3P+—0-, rather than H3P+═0

Semipolar P-O and P-C Bonds. A Theoretical Study of Hypophosphite and Related Methylenephosphoranes

Structures, energies, and electronic structures as derived from integrated projected densities are presented from ab initio MO calculations of H3PO (1), H3PCH2(2), H2PO2- (3), OPH2CH2- (4), and H2P(CH2)2- (5). The results show that allylic conjugation is not important in 3, 4, and 5 and that the PO and PC bonds in these compounds are best represented as dipolar bonds with little double-bond character. Simple electrostatic considerations suffice to interpret many of the results obtained concerning structure and energy

The Effect Of Technology Use On Productivity Growth

This paper examines the relationship between the use of advanced technologies and productivity and productivity growth rates. We use data from the 1993 and 1988 Survey of Manufacturing Technology (SMT) to examine the use of advanced (computer based) technologies at two different points in time. We also are able to combine the survey data with the Longitudinal Research Database (LRD) to examine the relationships between plant performance, plant characteristics, and the use of advanced technologies. In addition, a subset of these plants were surveyed in both years, enabling us to directly associate changes in technology use with changes in plant productivity performance. The main findings of the study are as follows. First, diffusion is not the same across the surveyed technologies. Second, the adoption process is not smooth: plants added and dropped technologies over the six-year interval 1988-93. In fact, the average plant showed a gross change of roughly four technologies in achieving an average net increase of less than one new technology. In this regard, technology appears to be an experience good: plants experiment with particular technologies before deciding to add additional units or drop the technology entirely. We find that establishments that use advanced technologies exhibit higher productivity. This relationship is observed in both 1988 and 1993 even after accounting for other important factors associated with productivity: size, age, capital intensity, labor skill mix, and other controls for plant characteristics such as industry and region. In addition, the relationship between productivity and advanced technology use is observed both in the extent of technologies used and the intensity of their use. Finally, while there is some evidence that the use of advanced technologies is positively related to improved productivity performance, the data suggest that the dominant explanation for the observed cross-section relationship is that good performers are more likely to use advanced technologies than poorly performing operations.technology, productivity, JEL Classification: L1, L6, D92,

Exploring steric constraints on protein mutations using MAGE/PROBE.

When planning a mutation to test some hypothesis, one crucial question is whether the new side chain is compatible with the existing structure; only if it is compatible can the interpretation of mutational results be straightforward. This paper presents a simple way of using the sensitive geometry of all-atom contacts (including hydrogens) to answer that question. The interactive MAGE/PROBE system lets the biologist explore conformational space for the mutant side chain, with an interactively updated kinemage display of its all-atom contacts to the original structure. The Autobondrot function in PROBE systematically explores that same conformational space, outputting contact scores at each point, which are then contoured and displayed. These procedures are applied here in two types of test cases, with known mutant structures. In ricin A chain, the ability of a neighboring glutamate to rescue activity of an active-site mutant is modeled successfully. In T4 lysozyme, six mutations to Leu are analyzed within the wild-type background structure, and their Autobondrot score maps correctly predict whether or not their surroundings must shift significantly in the actual mutant structures; interactive examination of contacts for the conformations involved explains which clashes are relieved by the motions. These programs are easy to use, are available free for UNIX or Microsoft Windows operating systems, and should be of significant help in choosing good mutation experiments or in understanding puzzling results