RE: CCL: GEOMETRY QUESTION

[fredvc : at : esalp1.dnet.dupont.com]

The problem outlined below was recently proposed to the list for comment:
 Given a fragment A-B-C, one wishes to attach a fourth atom, D, with the
 available information being:
                 r(BD)
                 <(ABD)
                 <(CBD)
 how can one *uniquely* define the coordinates of D??
 There is not enough information to define D uniquely.  Consider the situation
 with the ABC fragment is constrained to the xy-plane:
                      A
                     /
                 D--B
                     \
                      C
 Unless the angles <(ABC), <(ABD), & <(CBD) sum to 360 deg., ther
 will be 2
 solutions for the coordinates of D, differing in the algebraic sign for the
 z-coordinate.  In order to uniquely locate D one needs one additional piece
 of information.  Two possibilities are:
         out-of-plane angle (signed) for the BD bond
         dihedral angle A-C-B-D (signed)
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                            FREDERIC A. VAN-CATLEDGE
                             Sr. Research Associate
 Scientific Computing Division         ||   Office: (302) 695-1187 or 529-2076
 Central Research & Development Dept.  ||
 The DuPont Company                    ||      FAX: (302) 695-9658
 P. O. Box 80320                       ||
 Wilmington DE 19880-0320              || Internet: fredvc : at :
 esvax.dnet.dupont.com
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