unrestricted singlet

[Matthias Krack]

Hi William,

On Mar 19, 9:42 am, William <waile... at googlemail.com> wrote:
> Dear all,
>
> I want to know if it is possible to calculate unrestricted singlet
> state using cp2k.

You may use

UKS
MULTIPLICITY 1

for an unrestricted singlet.

> I saw the O2 triplet input in QS test directory. The triplet case is
> okay. But I tried an unrestricted singlet using the following
> settings, it crashed.
> ==================================
>     MULTIP 1
>     ROKS
>     &LOW_SPIN_ROKS
>        ENERGY_SCALING 1.0 -1.0
>        SPIN_CONFIGURATION 1 2
>        SPIN_CONFIGURATION 1 2
>     &END
> ==================================
>
> Can anybody tell me if the setting is incorrect or due to other
> reason?

I have two questions, besides the issues of input syntax:
Why do want to use Restricted Open KS to calculate an unrestricted
singlet?
What's the difference between a ROKS singlet and the RKS one in the
case of O2?

Matthias

> Many thanks in advance!
>
> Best,
> William