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Expected Accuracies

For anyone considering carrying out ab initio calculations of vibrational spectra, or simply interested in a thumbnail critique of a given paper in the literature, it would be particularly useful to have at hand some information as to what level of accuracy might be expected with a given basis set. We therefore take a brief interlude to explore this question for the dimers of HF and H2O, since both of these cases have witnessed the heaviest barrage of all levels of theory over the years. [Pg.171]

A comparison of a broad range of basis sets, varying from minimal to quite extended, was carried out several years ago for the HF and water dimers . The limitation of this study is that it did not go beyond the SCF level, nor did it include anharmonicity, so comparisons with experiment are tenuous. Nevertheless, the data do illustrate the trends and provide useful information as to the types of errors likely to be incurred for a H-bonded system with any given basis set type. [Pg.171]


The minimum wall thickness found with a manual ultrasonic wall thickness meter was 4.0 mm ( 2.3 mm wall thickness loss). This is in good accordance to the estimated wall thickness loss by radiography, which shows for small spots even a higher loss up to 2.8 mm. The expected accuracy for these measurements is about 0.2 mm. [Pg.566]

Determine the uncertainty for the gravimetric analysis described in Example 8.1. (a) How does your result compare with the expected accuracy of 0.1-0.2% for precipitation gravimetry (b) What sources of error might account for any discrepancy between the most probable measurement error and the expected accuracy ... [Pg.269]

This is only 5% of the original and still within normal expected accuracy of this method. For improved accuracy, the physical properties, R, h , and diffusivity K(j, could he recalculated for the conditions of this interval. This particular prohlem does not seem to warrant the extra work, although many problems may require a recalculation at every interval or two. [Pg.153]

For practical purposes, implicit schemes are the methods of choice when the solution is smooth and well behaved as a function of time. In that case much larger time steps can be taken than with explicit schemes, thus allowing a reduction in the computational effort. When large temporal gradients and rapid variations are expected, accuracy constraints set severe limits to the time-step size. In that case explicit schemes might be favorable, as they come with a reduced numerical effort per time step. [Pg.156]

The average value of rel at 310 K is 0.9 kcal/mol, so a comparison can be made between the trajectory and experimental results in Figure 8. The trajectory plots for re. of 0.5 and 1.0 kcal/mol have slopes (i.e. k Jk ) which are 1.6 and 2.0 times larger, respectively, than the slope of the experimental plot. Thus, if the same value of is used to deduce k s from the trajectory and experimental slopes, the trajectory k s will be larger than the experimental k by the above ratio of slopes. Given the expected accuracy of the trajectory results,52 the agreement between the trajectories and experiment is quite good. [Pg.150]

Due to the fact that the measurands are stochastic variables an uncertainty propagation analysis was carried out. An uncertainty analysis can answer two questions (1) the expected accuracy (uncertainty) of the method, that is, the expected uncertainty with respect to the sought quantity (2) the most uncertain (sensitive) measurands. [Pg.31]

For many compounds, experimental results arc available only over a narrow temperature span In these eases, estimation methods have been used to extend (he data over a more useful temperature range. When estimation methods have been used, the extent, method, and expected accuracy have been explained Thus, the user is aware of the reliability ol the graphical values. [Pg.4]

The above values of Ea and Ca f°r iton oxide can be used to predict heats of adsorption with other bases of known Eg and Cg. The heat of adsorption of ethyl sulfide should be -8.1 Kcale/mole, tetrahydrofuran -6.3 Kcal/mole, and p-xylene -2.6 Kcal/mole the expected accuracy of such predictions is 0.2 Kcal/mole. [Pg.85]

The QSAR is acceptable for the prediction of the acute toxicity to Pimephales promelas of organic chemicals, considered to act by the non-polar narcosis mechanism of action. The range of acceptable log Kow values for which it can be applied is from -1.24 to 5.13. The coefficient of determination (r2 value) of the model is 0.9, and its expected accuracy (95% prediction interval) is 0.64 log unit... [Pg.439]

Each of these factors is dependent on the other two, and the failure of any one of them can affect the accuracy of a weighing. For example, do not expect great accuracy from a balance that is located above a radiator. Likewise, do not expect accuracy from a balance which has just demonstrated poor precision. Finding the source of errors in weighing is a step-by-step process. You must rule out each problem before moving on to the next level. [Pg.123]

When the copolymerization is carried out under real conditions, each researcher is to answer a question which kinetic model is preferable for the proper description of the experimental data. One should also know the validity of the model under consideration, the numerical values of its parameters, and the expected accuracy of the calculated copolymer characteristics predicted within the framework of this model. Modern experimental methods for analyzing the copolymer composition... [Pg.54]

We see that the expected accuracy of A a is much lower than the errors of measurement and that this arises principally because of the small reaction interval chosen. [Pg.88]

In this section we will briefly consider a few questions concerning the expected accuracy of trajectory calculations in the context of unimolecular dissociation processes. For a particular molecular system it depends on the size of the system (number of atoms), the energy regime, the nature of the classical motion (e.g. regular or chaotic) and, very importantly, the timescale. These issues will be addressed in the following discussions of both random and non-random excitation of molecules. [Pg.224]

Our objective here is to try to answer the following questions For a proposed type of gas-liquid contactor compatible with the properties and flow rates of the phases and with the reaction type, what are the likely values of the specific interfacial area and the gas and liquid mass-transfer coefficients by which the contact performance can be predicted And what is the expected accuracy of these values Table XVIII gives typical values of these parameters in typical contactors shown in Fig. 12 for fluids with properties not very different from those of air and water (especially, liquid viscosity under 5 cP where the liquid is nonfoaming). Because this review is especially concerned with the chemical method of determining these parameters, experimental data obtained by this method will be given in subsequent tables and figures. [Pg.67]

Use a Web search engine such as Google to find sites dealing with potentiometric titrators. This search should turn up such companies as Spectralab, Analyticon, Fox Scientific, Brinkmann, Metrohm, Mettler-Toledo, and Thermo Electron. Set your browser to one or two of these and explore the types of titrators that are commercially available. At the sites of two different manufacturers, find application notes or bulletins for determining two analytes by potentiometric titration. For each, list the analyte, the instruments and the reagents that are necessary for the determination, and the expected accuracy and precision of the results. Describe the detailed chemistry behind each determination and the experimental procedure. [Pg.629]


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