NRVS Parameters
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Dialog Box: NRVS Parameters [Settings menu, Spectra Plotting Parameters]

See Spectra Window for details of NRVS spectra.

The file name from which the current NRVS observed (if any) has been read is shown.

Read button. This will read a file with the data for an observed NRVS spectrum. Each line in the file must be a data point. The energy in meV should be in the first column (first number on each line), and you can specify which column contains the actual scattering intensities.

Divide by frequency. The peak heights in experimental NRVS spectra are inversely proportional to energy or frequency, but this dependence on frequency is sometimes removed in data processing. If this box is checked, the spectrum will show the fraction of kinetic energy in the iron atoms, divided by frequency, as in the "raw" data. Note that the NRVS values in the Output are not divided by frequency.

Normalization. This specifies how the values in the observed data (entered by reading a file, above) are scaled or normalized to give an overall match to the observed. The factors or coefficients from the last redraw of the Spectra Window are shown below the options. There are currently three options:

--- Maximum to full. This applies a single scale factor to make the maximum value in the observed equal to the maximum value of the calculated. Note that the maxima for the calculated and observed do not necessarily occur at the same mode or frequency.

--- Integrated Intensity. This applies a single scale factor to the observed to make the total intensities, calculated at each of the wavelengths specified by the minimum and maximum frequencies and the frequency interval, equal. Observed values are interpolated if necessary, and maximum and minimum may be taken from the observed if these do not extend as far as the specified frequencies.

--- Fixed factor. The specified factor is applied to the observed.

Lineshape. The theoretical lineshape is Lorentzian, but broadening of various kinds typically produces a lineshape that is effectively Gaussian. The Voigt lineshape is a Gaussian convolution of Lorentzian lines - an approximation to it is used in many real-life situations in which the lineshape must be fitted rather closely. If Voigt is chosen the intensity contribution from a given mode is simply a linear combination of Gaussian and Lorentzian terms, with the line width in common between the two terms. Gaussian in Voigt is the fraction applied to the Gaussian term - this fraction is applied to all modes. See
P. Thompson, D.E. Cox, J.B. Hastings, J. Appl. Cryst. 1987, 20, 79, for details of this approximation to the Voigt profile.

Use dashes in black/white. The observed curve may be drawn dashed in black-and-white output, with the specified repeat length and dash/blank ratio.

Show bars only. If this box is checked, the calculated curve will not be shown, only the bars. The specified Normalization option will still be used, comparing the observed to the calculated curve.

Orientation to show in Spectra Window. This could be the spatial average, or any of three other orientations if present (usually x, y and z). This can be changed in the Spectra Window itself

Observed spatial average spectra group

This controls the input of observed spatial average NRVS spectra for multiple isotope configurations. The isotope configurations themselves are set up in the Isotopes - Multiple Spectra dialog, accessed with the Isotopes button in the Control dialog or from the Input menu.. That dialog also controls whether each of the configurations is calculated and refined by least-squares. You can read a file or delete the data for each configuration. In the data files, frequency is expected to be in column one, and the data in the column specified in the Read from column field to the right.

Observed spectra for orientations group

This controls the observed data and parameters for different orientations of a single isotope configuration (just now, only the first or main configuration). The Read and Delete buttons operate as for the spatial average data, and the Read from column field applies here as well.

When the Normalization mode is set to Fixed factor, the Scale factor entered here for each orientation is used instead of the Fixed factor entered in the Normalization setting. If the orientations differ from the Cartesian axis orientation used by VIBRATZ (which can be changed with the Pre-Calculation Rotations option in the Input menu), the Theta (angle of the x axis from the z axis) and Phi (angle of the plane of the y and z axes from the x axis) values can be changed. The default values of theta and phi are: x - 90,0; y - 90, 90; z - 0, 90. The angles values should be checked to be sure that bad values have not got in somehow.

The first or Average line in this group is essentially the same as the Iso configuration 1-main in the Observed spatial average spectra group - the Read and Delete buttons operate on the same data, and changing the Scale value also changes the Fixed factor value in the Normalization group and vice-versa.

At the moment it is assumed that either spatially-averaged data for different isotope configurations, or orientation data for the first or main isotope configuration, will be refined by least-squares, but not both. This is controlled by the Refine drop-down box in the Control Window.

The NRVS fractions for all orientations including the average can be obtained in a single calculation (solution of the normal equations), so the frequency intervals are required to be the same (that is there is only one set of frequencies for all orientations). When a new file is read in, if the frequencies do not agree within 0.1 cm-1 at the maximum frequency of the new data, the observed intensities will be linearly interpolated. You can choose whether to use the frequency intervals of the new data or of the old. It is assumed that frequency intervals are uniform in each spectrum.