*From*: Ian Hovell <HOVELL "-at-" cetem.gov.br>*Subject*: Problems with convergence - Summary*Date*: Fri, 4 Apr 2003 13:42:06 -0300

Dear CCLers, Monday last I asked a question to the group about the use of scipcm in g98w over the fact that it wouldn't converge. The replies that came back seemed to indicate that there was a bug in this version with this calculation. So after attempting the work a rounds kindly suggested by the group and failing in all cases I wrote to the Gaussian help people who replied the same day with the solution. I have pasted their reply below. Let me also publicly apologise for suggesting that there was a bug in g98W. I may have an old user's reference which is the second edition. ++++++++++++++++++++++++++++++++ Dear Dr. Hovell, There is not a bug in g98, but rather a change in the default behaviour. You can get the same results as from g94 with g98 by specifying a few extra options. I am appending my SCI-PCM frequently-asked questions entry which explains some of the extra input options available. If this does not help, let me know and I'll try to help. Regards, Jim Hess P.S. the difference between g98 and g94 is the scaling of polarisation charges - how to change this behaviour is explained below. ++++++++++++++++++++++++++ James Hess, Ph.D. Customer Support Scientist Gaussian, Inc. e-mail: help "-at-" gaussian.com <mailto:help "-at-" gaussian.com> ++++++++++++++++++++++++++ SCI-PCM frequently asked questions (1/30/02) Q. I've tried scrf=(scipcm,solvent=dichloromethane) and scrf=(scipcm,dielectric=8.93), but I always get the same result as when I don't specify the solvent. What's wrong with my input? A. The "solvent=<item>" option is only valid for PCM methods such as DPCM, CPCM, and IEFPCM. The "dielectric=<value>" option is only valid for Dipole (Onsager) model. For the SCI-PCM model, the input consists of a single line specifying the dielectric constant of the solvent and an optional isodensity value (the default for the latter is 0.0004). For example: #p pbe1pbe/6-31G* opt scrf=scipcm test ethene in dichloromethane 0 1 C C,1,CC H,1,CH,2,HCC H,1,CH,2,HCC,3,180.,0 H,2,CH,1,HCC,3,180.,0 H,2,CH,1,HCC,4,180.,0 CC=1.31477 CH=1.07363 HCC_1.8867 8.93 0.0004 Q. My SCI-PCM calculations always crash with the error: WARNING! Serious error in surface integrals. It is probable that some of the solute is outside the cavity and/or parts of the cavity surface cannot be reached from the origin. Try more integration points or a different set of integration origins. Surface Problems in SciFoc How do I add more integration points? A. There are several possible causes for this error and not all solutions involve the use of additional integration points. 1) You are using an effective core potential basis set. The combination of an ecp basis set and scrf=scipcm is problematic and not recommended. There is no reliable workaround at this time. 2) You are using a revision of G98 prior to Rev. A.11 and therefore the default behavior is to scale the polarization charges. This procedure is problematic and is no longer the default in Rev. A.11. To turn off scaling in earlier revisions requires some extra input on the same line as the dielectric constant and isodensity value. The following input is an example: #p pbe1pbe/6-31G* opt scrf=scipcm test ethene in dichloromethane 0 1 C C,1,CC H,1,CH,2,HCC H,1,CH,2,HCC,3,180.,0 H,2,CH,1,HCC,3,180.,0 H,2,CH,1,HCC,4,180.,0 CC=1.31477 CH=1.07363 HCC_1.8867 8.93 0.0004 302 1 3 F 0 The allowed values on the above line are summarized below: Input: Epsi Cont IPhi ITheta ISurf NoPrun IScal e.g. : 78.3 0.0004 40 20 3 F 0 --------------------------------------------------- Epsi = Dielectric constant of solvent Cont = Value of isodensity surface in atomic units. 0.0004 au is recommended and the default. IPhi = Number of phi values for numerical surface integration, or number of points in a Lebedev grid. Default is 302. ITheta = Number of theta Values for numerical surface integration, 1 to use a Lebedev grid, which is the default. ISurf = Whether to do surface integrals using a single origin (2) or piecewise, using Becke grids (3). 3 is most general and the default, but 2 is faster for convex cavities. NoPrun = Whether to not prune out close points in conductor scaled calculations. Default is False. Internally DoPrun = .not.NoPrun IScal = Whether to scale the polarization charges. 0=no. 1=yes, scale negative and positive charges separately and uniformly so that the total polarization charge equals -(1-1/epsi) times the charge of the solute molecule. This corresponds to localization of the solute charge distribution in the cavity. 2=yes, scale the polarization charges so that the TOTAL potential at all points on the cavity surface is zero when the medium is a conductor (epsi=infinity). Default is 2. Explicit derivatives of the scale factors are available for 0 and 2 only. 3) In some cases, this error does indeed mean that more integration points are necessary. To increase the number of integration points, change the values for IPhi and ITheta as described above. If you wish to use a Lebedev grid (the default), the allowed values of IPhi are 302, 434, 590, 770, and 974. The value of ITheta is always chosen as 1 when a Lebedev grid is desired. If you wish to use a general grid, choose any value for IPhi and ITheta. In cases 2 and 3 above, you should also consider using "scf=novaracc". This option uses full integral accuracy throughout the scf cycle procedure and can often aid in convergence. For cases which are exceptionally difficult to converge, it is often helpful to first converge the calculation with a diffuse isodensity value, for example 0.00004. After convergence is reached with the diffuse value, use this result as a guess for a calculation using a less diffuse isodensity. Ian Hovell - Ph.D. NUCLEO DE MODELAGEM MOLECULAR-NMM Centro de Tecnologia Mineral - CETEM Ministerio da Ciência e da Tecnologia- MCT Avenida Ipê, No 900 - Cidade Universitaria Ilha do Fundão Rio de Janeiro RJ Brasil CEP 21941-590 tel 00 55 (xx) 3865 - 7216 Fax 00 55 (xx) 22602837 ou 2290-4286 e-mail hovell "-at-" cetem.gov.br <mailto:hovell "-at-" cetem.gov.br> Ian Hovell - Ph.D. NUCLEO DE MODELAGEM MOLECULAR-NMM Centro de Tecnologia Mineral - CETEM Ministerio da Ciência e da Tecnologia- MCT Avenida Ipê, No 900 - Cidade Universitaria Ilha do Fundão Rio de Janeiro RJ Brasil CEP 21941-590 tel 00 55 (xx) 3865 - 7216 Fax 00 55 (xx) 22602837 ou 2290-4286 e-mail hovell "-at-" cetem.gov.br