[molpro-user] The smallest exponent that can be used to specify a basis function

[Tatiana Korona]

Dear Gerald,

A gaussian with the exponent equal to 1.E-50 has been used by Stanton and Gauss 
to obtain IP-EOM-CC3 energies directly from an EE-EOM-CC3 program, see 
J.Chem.Phys.,111,8785,1999, and ref. 18 there. If it were excluded by the 
program, then they wouldn't be able to calculate ionization potentials and make 
numbers for that paper. So, such a small exponent is certainly possible and 
_active_ in the program they used (probably Aces). I repeated this trick to 
obtain IP and EA with Molpro, but could use only the exponents like 1.E-12 for a 
continuum orbital. However, one can verify that this exponent is enough to 
provide a sufficient number of accurate digits for ionization potentials and 
electron attachments, e.g. I reproduced all digits given in papers on EA-EOM-CC 
methods.

You can test the following simple input

***, IP-EOM-CCSD (simulated with EE-EOM-CCSD)
memory,20,m

gprint,basis,orbital=10
zsymel=nosym
basis={
default,H=avdz,O=avdz
s,O,1.e-12
}
geometry={H1
           O,H1,R,              !Z-matrix for water
           H2,O,R,H1,THETA}
Theta=104                    !start bond angle
R=0.96 Ang                   !start bond distance

hf
ccsd
eom,-5.1,vir_orb=6.1 ! fix on excitations TO this orbital

This input will produce first 4 IPs for water. 6.1 is our zero-energy continuum 
orbital. However, if you change an additional exponent on oxygen from 1.e-12 to 
e.g. 1.e-15 or smaller, than you will get:

  ITERATION    DDIFF          GRAD             ENERGY        2-EL.EN. 
DIPOLE MOMENTS         DIIS   ORB.
     1      0.000D+00      0.000D+00     32025.50226135  64244.652599        NaN 
NaN        NaN    0    start
     2      0.000D+00      0.232D+02       -16.95078177     84.371664        NaN 
NaN        NaN    1    diag
     3      0.187D+02      0.165D+00     32657.17607612  65469.453071        NaN 
NaN        NaN    2    diag
     4      0.209D+02      0.106D+02     32655.12447108  65465.460273        NaN 
NaN        NaN    3    diag
     5      0.433D-01      0.108D+02     32649.67192410  65454.845120        NaN 
NaN        NaN    4    diag
  ?TOTAL ENERGY UNREASONABLE, ETOT =         0.32650D+05, ENEST = 
-0.75852D+02

in Hartree-Fock.

Best wishes,

Tatiana

On Sat, 11 May 2013, Gerald Knizia wrote:

>
> On Wed, 2013-05-08 at 11:41 +0200, Evgeniy Gromov wrote:
>> Gamess-US can converge SCF "hands down" with an exponent 1.E-50 .
>> Molpro however could do the same with 1.E-10. 1.E-15 or smaller
>> didn't work :(
>
> Unlike other programs, Molpro never throws away basis functions if they
> become unreasonable. Are you sure that your 1e-50 exponent basis
> function actually ended up the calculation? Because for such a function
> even handling its normalization coefficient would be a serious problem.
>
> While it is perfectly possible to calculate integrals over such
> functions[1] (it is even done routinely with zero exponent functions for
> implementing simpler integrals in terms of more complicated integrals),
> using them as basis functions is very much not recommended. If you want
> to try it anyway, be sure to turn off all integral screening,
> compression, and approximation options.
>
> [1] See JCTC 7 2387 (2011)
> -- 
> Gerald Knizia
>
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>

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


`The man who makes no mistakes does not usually make anything.'
                                        Edward John Phelps (1822-1900)