[molpro-user] doubly excited state

[Tatiana Korona]

I can only agree with Kirk. Although the EOM-CCSD program can formally 
calculate doubly excited states and founds them from time to time, these 
results cannot be trusted (errors of order of 1eV can be expected for 
states dominated by double excitations). The obvious exceptions are 
2-electron molecules: for them CCSD and EOM-CCSD are exact(=FCI). For that 
reason no mechanism has been built into the program to allow convergence 
to a specific doubly-excited state (for single-dominated states one can 
switch on the following mechanism, that finds a wavefunction the most 
similar to a sample - usually CIS - wavefunction).

Tatiana

On Mon, 19 May 2008, Kirk Peterson wrote:

> Lukas,
>
> unfortunately EOM-CCSD is not able to compute states corresponding to a true 
> double excitation.  The state must be dominated by a single excitation 
> relative to the ground state. You'll have to try MRCI or CASPT2.
>
> -Kirk
>
> On May 19, 2008, at 12:37 PM, Lukáš Félix Pašteka wrote:
>
>> Hello,
>> 
>> I have a problem computing doubly excited state. How can I tell MOLPRO to 
>> compute exact doubly excited state (two electrons from HOMO to LUMO+1)? I 
>> tried:
>> 
>> eom, -3.1, -3.2
>> eompar,inisingl=0
>> 
>> which computed few states but not the one I am interested in. I would be 
>> grateful for any advice. Thanks in advance.
>> 
>> Lukas Pasteka
>

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)