From mxm@iris80.biosym.com Fri Sep 10 14:02:50 1993 Date: Fri, 10 Sep 93 21:02:50 -0700 From: mxm@biosym.com (Max Muir ) Message-Id: <9309110402.AA22850@iris80.biosym.com> To: chemistry@ccl.net Subject: MOPAC6.0 ESP, Again Dear CyberChemists, Calcn. of ESP fitted charges with MOPAC6.0 _________________________________________ a collegue has been using MOPAC6.0's ESP option to get a set atom charges fitted (least squares) to a bunch of electrostatic potential points on Connolly surfaces at 1.4, 1.6,1.8 and 2.0 times the vdWs atom radius. Old hat, yes, but he is unable to reproduce the values that appear in Kolman's paper (J. Comp. Chem., Vol. 11, No. 4, 431- 439 (1990)) and neither am I. Consider the case of formaldehyde (does anyone call it methanal?). I'm using the default values for SCALE (1.4) NSURF(4) and SCINCR (0.2). Here's my input deck . . GRAPH NODIIS MMOK ESP SLOPE=1.422 POTWRT NOINTER PRECISE I shot an elephant in my pyjamas the other day C 0.000000 0 0.000000 0 0.000000 0 0 0 0 O 1.230000 1 0.000000 0 0.000000 0 1 0 0 H 1.090000 1 120.000092 1 0.000000 0 1 2 0 H 1.070000 1 120.000114 1 180.000000 1 1 2 3 The fitted charges are . . (from .out) ELECTROSTATIC POTENTIAL CHARGES ATOM NO. TYPE CHARGE SCALED CHARGE 1 C 0.3897 0.5541 2 O -0.3613 -0.5137 3 H -0.0142 -0.0202 4 H -0.0142 -0.0202 THE NUMBER OF POINTS IS: 375 THE RMS DEVIATION IS: 0.7655 THE RRMS DEVIATION IS: 0.0794 While Kollman et al report (in figure 1) the following MNDO charges. Formaldehyde H +0.006 C +0.339 O -0.352 The unscaled fitted charges aren't too bad, but the H's have changed sign. The scaled fitted charges seem incredible and your humble correspondent does not believe them. Have I missed something obvious? Yours faithfully, Max Muir From b_duke@lacebark.ntu.edu.au Sat Sep 11 09:07:36 1993 From: b_duke@lacebark.ntu.edu.au Message-Id: <9309112007.AA10781@lacebark.ntu.edu.au> Subject: Re: CASSCF and G92. To: CHEMISTRY@ccl.net (chemistry) Date: Sat, 11 Sep 1993 15:07:36 -0600 (CDT) Dear Chem-netters, Steven Bachrach writes: >I recently perused Feller's report comparing a variety of >computational codes and computers. One interesting point I >noted is that Gaussian-90 and Gaussian-92 both gave the >wrong CASSCF energy for ethylene using the 6-311++G** basis >set. Also, without naming names, at the Chicago ACS meeting, a >reliable source told me that the CASSCF routines in Gaussian >are wrong. >Without generating a major flame war, what is the general feeling >concerning the CAS codes in Gaussian? My only experience with CAS >was that the original makefile for G90 for SGI was incorrect - that >the -static flag needed to be included for the CAS links. I am not sure whether I have an example of a bug, but I have some points and some queries about G92 CSSCF that I was intending to put to the net. I am trying to do a doublet Au ground state where I suspect the ROHF or UHF reference determinant is not good enough for CISD, MPn, CCSD. In several cases CASSCF includes a configuration with the 3rd or 4th largest coefficient in the CI that is not, as far as I can see, Au. In every case at the end, even when I have not spotted a non-Au configuration (although I only check the 10 most important), it tells me it can determine the state. The orbitals (occ and active, at least) are given correct symmetry labels. Has anyone else seen something like this? In listing the configurations (at great waste of paper, if you print output) it gives SYMMETRY 0 opposite each. Under what circumstances, if any, does it say something useful here. In my example convergence is terrible. You can increase the number of iterations allowed by SCFCYC. I need about 150 iterations. Are there any ways of improving the convergence? Is there a way of decreasing the convergence criteria? It would be nice, for example, and this would be one way to do it, to get the CI weights after just one step so one can see whether the MCSCF is greatly increasing the weight of one configuration from the CI with the original ROHF or UHF natural orbitals reference. Is there a good reference to a discussion on selecting the active space? That seems enough questions to be going on with. Cheers from "down under", Brian. -- Associate Professor Brian Salter-Duke (Brian Duke) School of Chemistry and Earth Sciences, Northern Territory University, Box 40146, Casuarina, NT 0811, Australia. Phone 089-466702 e-mail: b_duke@lacebark.ntu.edu.au or b_duke@darwin.ntu.edu.au