Syntax of the Pick Statement

PICK $<$pick-statement$>$

is invoked from the main level of X-PLOR. Execution is activated as soon as all required statements are given.

$<$pick-statement$>$:==

ANGLe

$<$selection$>$ $<$selection$>$ $<$selection$>$ $<$property$>$ picks bond angle properties between selected atoms. Except for the GEOMetry property, each selection should select exactly one atom; for GEOMetry, the center of mass of each selection is computed, and then the angle between the centers of mass is evaluated. The result is also stored in the symbol $RESULT.

BOND $<$selection$>$ $<$selection$>$ $<$property$>$

picks covalent bond properties between selected atoms. Except for the GEOMetry property, each selection should select exactly one atom; for GEOMetry, the center of mass of each selection is computed, and then the bond between the centers of mass is evaluated. The result is also stored in the symbol $RESULT.

DIHEdral

$<$selection$>$ $<$selection$>$ $<$selection$>$ $<$selection$>$
$<$property$>$ picks dihedral angle properties between selected atoms. Except for the GEOMetry property, each selection should select exactly one atom; for GEOMetry, the center of mass of each selection is computed, and then the dihedral angle between the centers of mass is evaluated. The result is also stored in the symbol $RESULT.

IMPRoper

$<$selection$>$ $<$selection$>$ $<$selection$>$ $<$selection$>$
$<$property$>$ picks improper properties between selected atoms. Except for the GEOMetry property, each selection should select exactly one atom; for GEOMetry, the center of mass of each selection is computed, and then the improper angle between the centers of mass is evaluated. The result is also stored in the symbol $RESULT.

RING

{ $<$selection$>$ } $<$property$>$ picks the generalized pucker parameter of the selected ring as described by Cremer and Pople (1975). The ring is selected by specifying all atoms by multiple selection (Section 2.15). Each selection should refer to exactly one atom. At least four selections are required. There are $q=n/2-1$ amplitudes and $p=(n-1)/2-1$ phases where $n$ is the number of atoms of the ring. The amplitudes are stored in the symbols $AMPLITUDE1, $AMPLITUDE2, ...and the phases are stored in the symbols $PHASE1, $PHASE2, .... The number of amplitudes $q$ is stored in the symbol $N_AMPLITUDE and the number of phases $p$ is stored in the symbol $N_PHASE.

$<$property$>$:==

ENERgy

is the potential energy value of the corresponding partial energy term (does not apply to RING).

GEOMetry

supplies information about the actual value of the picked object (does not apply to RING).

PUCKer

applies only to RING.