From elewars@alchemy.chem.utoronto.ca Thu Jan 11 22:32:51 1996 Received: from alchemy.chem.utoronto.ca for elewars@alchemy.chem.utoronto.ca by www.ccl.net (8.6.10/950822.1) id WAA25431; Thu, 11 Jan 1996 22:30:32 -0500 Received: (from elewars@localhost) by alchemy.chem.utoronto.ca (8.7.1/8.7.1) id WAA26946 for chemistry@www.ccl.net; Thu, 11 Jan 1996 22:30:31 -0500 (EST) Date: Thu, 11 Jan 1996 22:30:31 -0500 (EST) From: "E. Lewars" Message-Id: <199601120330.WAA26946@alchemy.chem.utoronto.ca> To: chemistry@www.ccl.net Subject: REPORT ON A FREQ PROBLEM Hello, some interest was expressed in the problem (see below) I submitted to the Net a couple weeks ago. Some people suggested that the trouble lay in the symmetry changing during Spartan's numerical freq calc (C4v --> Cs), or in instability of the wave- function. I tried to test the wavefunc stability, but that calc flopped with a slew of "unable to assign spin for state..." messages. Since G92 gave the same, reasonable freqs with both analytical and numerical methods, I think the "large imaginary" Spartan freqs are represent a (rare) quirk in that program. The pyramidane and several of its derivatives are relative minima, with of sign of oddball freqs. ======================================== 1995 Dec 25 Hello, I have an interesting problem connected with Spartan. I did an opt/freq on the unusual molecule Me Me \ / Me /C\ Me C------ C \ // \ \ / | \ / | \ /-/------\-\ / | C | C(C-Me)4 Tetramethylpyramidane [/__________\] | / \ | / \ C--------C NOTE: pyramidane, C(CH)4, is / \ / \ a relative minimum (no Me Me Me Me imaginary freqs) at the HF/6-31G*, MP2/6-31G* and C4v MP2/6-31++G** levels. (The HF/6-31G* geom was given in the original mailing) The HF/6-31G* opt proceeded normally (E=-347.628 348), but the freqs are absurd: -68748.51 E -68748.51 E -22116.22 A1 -11996.37 B1 (followed by sensible +ve freqs 151.29 B2 151.88 A2 etc.) ZPE = 566.02 kcal/mol Finding this hard to accept, I used the Spartan HF/6-31G* geom as input for a Gaussian 92 HF/6-31G* opt/freq. The Gaussian opt (which needed only one opt cycle) gave the same E as Spartan (-347.628 348 6) but the freqs and ZPE were quite different (the E from the freq job was also -347.628 348): +163.42 E +163.42 E +164.03 A2 +164.64 B1 +182.69 B2 etc ZPE = 120.42 kcal/mol Has anyone any idea why the two programs gave such different results? I presume that the "huge negative" freqs are simply wrong, and the Gaussian freqs are correct; the parent compound C5H4, and other substituted pyramidanes, gave normal freqs. Thanks for any suggestions. Errol Lewars