Gradient accuracy

Pump flow rate accuracy and gradient accuracy Detector linearity of response, noise, drift, and wavelength accuracy Injector precision, linearity, and carryover Column heater temperature accuracy... 

Pump flow rate range, gradient mixing mechanism, gradient accuracy, and solvent-delivering capability... 

Pump flow rate accuracy and gradient accuracy... 

Gradient accuracy 1% of the step gradient composition 6 months... 

The difference between experimental and programmed %B values of steps 1-5 is calculated for the judgement of the gradient accuracy. 

It is usually not efficient to use the methods described above to refine the transition state to full accuracy. Starting from a qualitatively correct region on the potential surface, in particular one where the Hessian has the right signature, efficient gradient optimization teclmiques, with minor modifications, are usually able to zero in on the transition state quickly. 

In order to conserve the total energy in molecular dynamics calculations using semi-empirical methods, the gradient needs to be very accurate. Although the gradient is calculated analytically, it is a function of wavefunction, so its accuracy depends on that of the wavefunction. Tests for CH4 show that the convergence limit needs to be at most le-6 for CNDO and INDO and le-7 for MINDO/3, MNDO, AMI, and PM3 for accurate energy conservation. ZINDO/S is not suitable for molecular dynamics calculations. 

Computational accuracy can be dramatically improved by dynamically adding elements where they minimize the error. For example, more elements ean be added in the neighborhood of a strong gradient in the velocity to help resolve shocks and vortex sheets. Elements may be removed from regions of smooth flow to minimize the computational cost without degrading the overall accuracy. The concept is shown in Fig. 9.6 where a finer mesh overlays the original mesh. This mesh refinement can be carried out to as many levels as necessary [15], [16], [17]. 

For many practical purposes sufficient accuracy is obtained by neglecting the leakage flow term. In addition the pressure gradient is often considered as linear so... 

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