Volume 2 Chapter 3 3D-Constrain Sub-menu PERMUTE

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SELECT is used to specify the allowed minimum and maximum values for a parameter which has already been defined using the DEFINE PARAMETER or TRANSFORM commands.

Only if the value of the parameter lies within this range will the crystal fragment be accepted as a hit.

QUEST3D applies the selection criteria in the order input by the user.


Suppose that we have defined parameter B1 as the distance between atoms 8 and 7.

Note the following:


  1. When specifying the limiting values real numbers or integers may be used.

  2. When specifying limiting values for a torsion angle the following rules apply:

    The torsion angle A-B-C-D is the angle by which the vector A-B must be rotated to overlie the vector C-D when viewed along the vector B-C from B to C.

    According to the convention of Klyne and Prelog (Experientia 16, 521, 1960):

    The selection range for a torsion angle parameter is interpreted by QUEST as including those torsion angles within the segment formed by a clockwise rotation from the first limiting value to the second.

    Limiting values must be specified with the second value greater than the first, eg. -160 -140

  3. Special care should be taken when specifying limiting values for:

    One cannot predict in advance whether the calculated angle will be the "expected" value or its supplement. To cater for this situation one might choose to obtain the acute value in all cases.

    Suppose the defined angle has been named ?ANG


    set ?SIN = SIN ?ANG
    set ACUTE = ASIN ?SIN

    where ?SIN is the sine of ?ANG, ACUTE is the arcsine of ?SIN.

    Apply the SELECT limiting values to ACUTE.

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    Volume 2 Chapter 3 3D-Constrain Sub-menu CENTROID.