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CCL:G: Dioxane in PCM with G03 -------------------------------------------------------------------------------- From: Madi Subject: CCL:G: Dioxane in PCM with G03 Date: Thu, 14 May 2009 17:17:29 -0400 -------------------------------------------------------------------------------- Sent to CCL by: Madi [madi7sk{:}gmail.com] Hi, I was trying to specify DMF using the PCM model in gaussian and was having trouble getting it to work. I wrote to gaussian and their reply was very helpful. I am attaching it here for your reference. After you are done specifying all the parameters, make sure you deliberately leave a blank line. Hope this helps madi ****************************************************************** Regarding the specification of the DMF solvent, even though only the solvents listed in the Gaussian documentation of the SCRF keyword are available through the "Solvent=" option, a different solvent may be explicitly defined in the PCM input. However, please, note that it is not possible to input all parameters that define an arbitrary solvent. Specifically, one cannot define all of the terms necessary to calculate the non-electrostatic contributions. For this reason, there are two recommended alternatives: 1) Check in the list of solvents provided for the SCRF keyword whether there is a solvent similar enough to the one you would like to use in your calculation and provide this name in the "Solvent" option of the SCRF keyword. Then, add also the "Read" option to provide the modifications of "EPS", "RSOLV", "Density", and "VMOL". This way, you would be introducing the parameters for your desired solvent, for the cases of parameters that are available for user input, and the program would be using the closest possible parameters for those other parameters that are not available for user input. (Note: if no solvent is specified, then the program defaults to water). So, probably, your best choice here would be to select a solvent with similar properties to DMF (such as Acetonitrile, DMSO, Acetone, Nitromethane) and then give the corresponding "EPS", "RSOLV", "Density", and "VMOL" parameters for DMF. 2) Alternatively, you can use the options "NoDis NoRep NoCav" in order to prevent the use of the parameters for the internally stored solvent (water, by default), so the non-electrostatic contributions to the solvation energy will not be computed. Note also that this is true if the default "UA0" radii are used, the electrostatic terms are then correctly computed this way. If this is not the case, and the UAHF or UAKS radii are used, then there is a dependency of the radius with the type of solvent so it would not be correct to use a modified water as a model for a solvent with properties different than water. Thus, if UAHF or UAKS radii are used, then one has to still do what it was explained in the previous paragraph, 1), (that is to use the "Solvent=" option to select, from the list of predefined solvents, a solvent similar to the one you are interested in). For the calculation of only the electrostatic part, you can define the solvent by defining the dielectric constant using the "EPS" option, the solvent radius using the "RSOLV" option, and the dielectric constant at infinite frequency using the "EPSINF". EPSINF is the dielectric constant at infinite frequency. It is an experimentally measured value. The value of EPSINF will not affect the results of ground-state energy calculation of DeltaG(solv), so you do not need to worry about getting a non-standard value. EPSINF is only necessary when performing excited state PCM calculations. Other than EPS, RSOLV usually makes the biggest difference in the result. As for choosing a value of RSOLV, our developers recommended a couple of references they use for this parameter: * O. Sinanoglu in "Molecular Interactions" Z. Ratajczack and Orville-Thomas eds, Wiley 1982 vol. 3 chap. 6 * M.H. Abraham and A. Nasehzadeh J. Chem. Soc. Faraday Trans. 1 1981, 77, 340. If the desired RSOLV parameter is not found there, the molar volume may give some hints for RSOLV values for new solvents, even though attention must be paid to the chemical nature of the solvent, because strong interactions modify, to some extent, the definition of the hard sphere analogue of the solvent molecular volume. Thus, although a simple approximation, the Stearn-Eyring formula (Stearn, Eyring J. Chem. Phys. 1937, 5, 113) can be used to derive a value for RSOLV, given the molar volume of the solvent. Finally, about other parameters, which only affect the non-electrostatic terms, the DENSITY is a "number density", i.e. number of particles per volume, and the units are Angstroms^¨C3. Taking the density of the solvent in "g * cm^¨C3", divide by the molar weight of the solvent and multiply by Avogadro's number to transform the grams into number of particles, and, finally, divide by 10^24 to transform cm^¨C3 into Angstrom^¨C3. Although the density and the molar volume are obviously related, these two quantities are used by the program to compute two different energy contributions and, unfortunately, they were introduced in the code as two independent parameters. Thus, the user needs to provide both the density ("DENSITY" PCM keyword) and the molar volume ("VMOL" PCM keyword) in order to set the desired modifications, so the two of them are consistent with each other. The units of the density are Angstrom^¨C3 while the units of the molar volume are cm^3. So, from the value of the density of the solvent in "g * cm^¨C3", take the inverse of the density and then divide by the molar weight of the solvent in order to get the molar volume in cm^3. Enter this parameter in your input file with the "VMOL" PCM keyword. The following input will use the standard parameters for the solvent given in "Solvent= additional PCM options (the values given below are not representative of any particular solvent and they are only given as an example of how to use these keywords): % #P SCRF=(PCM,Solvent= EPS=6.0 RSOLV=1.6 DENSITY=0.045 VMOL=19.05 [zz] http://www.ccl.net/cgi-bin/ccl/message-new?2009+05+14+009 |
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yjcmwgk(½ð±Ò+2): 2010-03-24 19:08
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4Â¥2010-01-27 15:59:47
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