[molpro-user] E2exdisp in CCSD-SAPT converges to the wrong value in DC+BS

[Tatiana Korona]

Dear Leonid,

my result for your no-df input with one line modification gives:

E2disp=-2.907495
E2exdisp=0.473707

You have not set your artificial beryllium atom to dummy before the first part 
of the calculation, therefore a wrong Enuc has been found for the dimer.

This was the main problem present in both inputs.

Additionally, for the DF case you should provide a more sensible auxiliary 
basis set on dummy. Note that an auxiliary basis should describe PRODUCTS of 
the atomic basis.

Best wishes,

Tatiana

On Thu, 22 Sep 2016, Leonid Shirkov wrote:

> Hello Molpro Community,
>
> I was running some test jobs to calculate E2disp and E2exdisp energies
> for He2 with
> CCSD-SAPT at R=3.0 bohrs  (interatomic distance).  In order to speed
> up the convergence
> I employed midbond functions, and that works well for E2disp. However,
> E2exdisp converges
> to a smaller wrong value if DC+BS is used. Without the midbond
> functions, i.e. with DCBS,
> it converges to a value that  agrees well with  the previously
> reported CCSD-SAPT calculations,
> see 10.1063/1.2889006 and  10.1021/ct900232j.
> These values are Edisp=2.937 and E2exdisp=0.479 (mhartree units).
>
> Here is the outline of the results, '+' denotes the midbond functions,
>
> without density-fitting:
>
>             Edisp  Eexdisp
> avtz       -2.599   0.391
> avdz+    -2.884   0.165
> avtz+     -2.907   0.235
> avqz+    -2.940   0.261
>
> with density-fitting (avXz/mp2fit used as the auxilary basis set):
>
>           Edisp  Eexdisp
> avtz     -2.600   0.383
> avqz    -2.853   0.454
> avdz+  -2.894   0.087
> avtz+   -2.910   0.103
> avqz+  -2.937   0.115
>
> I am attaching the inputs that I used for DC+BS calculations, both df
> and non-df versions.
> Is there anything wrong with my inputs? Perhaps some input parameters
> or thresholds ought
> to be tweaked? Increasing the integration grid by the 'dispgg' parameter to
> 20 does not help. Just in case it matters, I am using the 2012.1 version.
>
> I would appreciate any help and insight.
>
> Leonid
>

Dr. Tatiana Korona http://tiger.chem.uw.edu.pl/staff/tania/index.html
Quantum Chemistry Laboratory, University of Warsaw, Pasteura 1, PL-02-093 Warsaw, POLAND