Re: CCL:Z matrix to cartesian coord. Question



 On Dec 8,  2:27pm, Charles G. James wrote:
 > Subject: CCL:Z matrix to cartesian coord. Question
 > I do not mean this as an attack upon anyone or anything.  However this
 relates
 > to information I have to pass on to undergraduates in reference to
 > computational chemistry.  Just this week someone on this mailing list asked
 for
 > a way to get 10-15 (significant?) digits, after the komma(decimal),
 Cartesian
 > coordinates for a Ih symmetry molecule from the z matrix of a Gaussian
 > 92 program. Are we at the stage where that many significant digits are
 given
 by
 > any computational chemistry method?  Are we at the stage where that many
 > significant digits are obtainable by any physical method used to measure
 > structure?  I am still warning undergraduates to beware of the number of
 digits
 > which can appear in calculations not connected to their measurements or
 their
 > original input.  Can I now say there are ways out there to get precision
 only
 > formerly dreamed by spectroscopist? Are there ways to get structural
 parameters
 > to this precision?
 >
 > Charles G. James, Jr.           Assoc. Professor of Chemistry
 > Dept. of Chemistry,  University of North Carolina at Asheville
 > Asheville, NC 28804-3299, USA             Phone: (704)251-6443
 > FAX: (704)251-6041                     E-mail: james { *at * } unca.edu
 Prof. James,
 I believe you misunderstood the intent of the message you referred to. The
 author wanted his high symmetry geometry to be converted from internal to
 cartesian coordinates to 10-15 digit accuracy. The reason for this is not
 that the structures are assumed to be good to this many decimal places, but
 that programs that figure out symmetry from cartesian coordinates very often
 need the symmetry exactly or nearly exactly before there are able to pick
 it up. My interpretation is the standard 6 decimal places he has from his
 g92 output file is not accurate enough for the program he is subsequently
 using for it determine or to verify that the molecule really is Ih symmetry.
 Bill
 --
 ******************************************************************************
 *    "Like jewels in a crown, the precious stones glittered in the queen's
 *
 *     round metal hat." - Jack Handey
 *
 *                                                                            *
 *     Bill Laidig                                                            *
 *     The Procter & Gamble Co.             tel 513-627-2857 fax - 1233
 *
 *     Miami Valley Laboratories            laidig { *at * } pg.com (preferred)
 *
 *     P.O. Box 538707                      laidigwd { *at * } pg.com
 *
 *     Cincinnati, OH 45253-8707            laidig { *at * } qtp.ufl.edu
 *
 ******************************************************************************