Some question about basis set

[manyu]

 

 Question1:

         Turbomole provide some basis such like SV,TZVP, now  I wonder is there any stander basis like 6-31g , I try to do same simple  task to compare the results to other software like G03, but I cannot get the same result without the same basis. 

 Question2:

         I plan to do some complex job with my own basis , how can I use my own basis in Turbomole?

[antti_karttunen]

Hi,

Question 1: Turbomole basis set library also includes some basis sets of Pople and coworkers. For example, 6-31G can be used in Define by entering
b all 6-31g hondo
For hydrogen there is no 6-31G in Turbomole library, but you can use "4-31g hondo", which is identical to 6-31G in the case of hydrogen. You can examine the Turbomole basis set library in $TURBODIR/basen to see what basis sets are included by default. $TURBODIR/basold contains additional (old) basis sets.

Note that Gaussian includes the Karlsruhe SV, SVP, TZV, and TZVP basis sets for several elements, so you can also perform comparisons by using them.

Question 2: Before starting Define, create a file that contains your own basis set in Turbomole format. The format is very simple, so manual conversion is the most straightforward way. You can look for example from the "basis" file normally created by Define. For example:

$basis
*
c mybas
# Comment line. The "c mybas" tells Turbomole that this is "mybas" basis set for element C
*
<basis set definition for c>
*
h mybas
# Another comment line
*
<basis set definition for h>
*
$end

Give the basis set file a name you remember (for example mybasen). Start Define and in basis set menu enter command "b all mybas". Define says that it cannot find the basis, so you must use the "file" command in the new submenu. Enter "file ./mybasen" and Define should find your basis set (if the basis set file was located in the directory you started Define. Otherwise you have to give the full path to "file"). Define asks the location of "mybas" for each element.

If you plan to use your own basis set often, you can also create your own basis set library. See the Turbomole tutorial: http://www.cosmologic.de/data/Turbomole_Tutorial_59.pdf

[uwe]

Hi,

just some general remarks about the comparison of total energies or properties from different quantum chemistry programs:

1. Basis set

    it is obvious that you have to use the very same basis set, that's what you were asking for.

2. DFT functional

    many people try to compare DFT results, so make sure that you are really using the very same functional. With Gaussian, you could either use  VWN 5 instead of the Gaussian default VWN 3 for all functionals that include VWN (like B3-LYP), or use the VWN 3 functional within Turbomole instead of the default VWN 5 (only possible for B3-LYP).

3. DFT grid size

   Gaussian and Turbomole are using completely different numerical integration grids for the DFT quadrature. So comparing just the number of grid points is not sufficient.

4. RI

   Do not switch on RI in Turbomole if you want to compare the total energy to Gaussian. And I am not sure if Gaussian's version of RI (they call it density fitting) gives the very same results as Turbomole if you are using the Turbomole auxiliary basis set for both programs. That would be nice to know, so if you are going to try it, please tell us  .

5. SCF convergence criteria

   That is a  bit more tricky, because the number of SCF iterations and the total energy both depend on the thresholds for neglecting integrals. In Turbomole, you can change $scfconv for the energy convergence and $denconv for the density convergence. The integral neglect threshold is determined by those two keywords (more or less), but the actual threshold when evaluating the integrals does also depend on several other things like the sum of the l-quantum numbers of the integral...
I have no idea how you can change the threshold in Gaussian, or how to compare it at all, but both programs will print some number in the output...

6. Geometry convergence criteria

   Turbomole has two optimizer: relax and statpt. The default, when calling jobex, is to use relax. relax just checks for the difference in energy and the gradient norm. If you call jobex with -statpt, then the (newer) optimizer statpt will be used. statpt checks for the energy change, RMS of displacement, RMS of gradient, the maximum displacement and the maximum gradient. The number of geometry cycles will, of course, depend on all those thresholds. Please make sure that all thresholds that are used in both program packages are the same.

7. Start geometry

   Gaussian automatically moves a molecule in its center of mass - Turbomole does not (unless you do not have C1 symmetry, or unless you are using internal coordinates during an optimization - then, the information about the absolute position is lost after the first geometry cycle due to the transformation from internal to cartesian coordinates). That has no effect on energy or gradients. But if you do something like NMR chemical shieldings, the GIAO integrals are defined by a vector that points from the origin to the atoms. If your input structure is far away from the origin, the numerical errors of the GIAO integrals might get quite large, and the different contributions to the shielding tensor do not cancel each other completely. Move your structure to CMS before starting such a calculation (within define, in the first menu, say 'm' for 'manipulate geometry', and then 'inert').


Hence, I would just compare the Hartree-Fock single point energy on the same input structure, using the same basis set, without RI/density fitting...

Regards,

Uwe