Standard Orientation Geometry

This section displays positioning of the atoms in the molecule used by the program internally, in Cartesian coordinates. This orientation is chosen for maximum calculation efficiency, and corresponds to placing the center of nuclear charge for the molecule at the origin. Most molecular properties are reported with respect to the standard orientation. Note that this orientation usually does not correspond to the one used in the input molecule specification the latter is printed earlier in the output as the Z-matrix orientation.  

Exploring Chemistry with Electronic Structure Methods 

The molecule is positioned in the YZ-plane, with the C=0 bond coinciding with the Z-axis. 

The total energy of the system, computed at the Hartree-Fock level, is given by this line of the output  

The value is in hartrees. The number of cycles it took the SCF calculation to converge is also given on this line (refer to Appendix A for a discussion of the iterative nature of the SCF method). When we discuss energies in this work, we will generally use hartrees (atomic units) when we discuss energy differences, kcal-moT will often be a more convenient unit (especially when comparing calculation predictions to experimental results). 

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With this outlook, the key factors appear to be the coincident occurrence of SO2 and moisture. The controlled metal exposures from the ASTM studies were of flat panels in standard orientation. The simple geometry avoids many complications from moisture retained in surface texture features. Therefore, as a first approximation, we take the relevant time of wetness to be short periods following precipitation and periods of dew formation. The formation of a film of water is most likely at high relative humidities high humidities are most prevalent during the night hours. In the eastern U.S., summer predawn humidity is typically 80-90% compared to afternoon humidities of 50-60% winter patterns are less pronounced in areas north of the Ohio river, but also show afternoon minima (3) ... 

Finally, the time that a specimen is wet depends on sunlight heating, prevailing winds, and specimen geometry. Specimen orientation is, therefore, much more critical in atmospheric galvanic corrosion testing. Standard orientations are specified in ASTM G 50 as 30° to the horizontal facing south or the nearest source of corrodent (the sea). 

FIGURE 14.26 Space-filling model for 51D (X=F) obtained by full geometry optimization at the HF/6-31(d) level of theory and shown in the Gaussian standard orientation. 

Research users need full access to the functional elements of the spectrometer system and require the most efficient and flexible tools for MR sequence and application development. If the measurement methods delivered with the software do not adequately address the specific investigational requirements of a research team, modem NMR software is an open architecture for implementing new and more sophisticated functionality, with full direct access to all hardware controlling parameters. After evaluation, the new functionality can be developed with the help of toolbox functions that allow rapid prototyping and final builds, to enable the new sequence to be executed by non-experienced personnel and then used in routine applications. These toolboxes provide application oriented definitions and connect to standard mechanisms and routine interfaces, such as the geometry editor, configuration parameters or spectrometer adjustments. 

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