Subject: RE: CI-Singles - Wrong Excited State Energies?

From: "Phillip Matz" <[email-masked]>
Date: Wed, 12 Dec 2001 00:05:13 -0800

When you refer to the excited state geometry as being higher in energy are
you referring to the transition energy (GS -> ES Delta Energy) or the
absolute energy of the same excited state computed with different nuclear
geometries?

What should happen is that the absolute energy of the excited state for
which you are optimizing the geometry decreases as the forces are minimized
relative to the excited state wave function.  The nuclear relaxation
accompanying the excited state optimization will only raise the ground-state
wave function's energy resulting in an apparent red-shift in the gas-phase
emission spectra (by definition, otherwise the ground-state nuclear geometry
was never optimized).

Thus, comparing the energy of the lowest excited state (ES1) determined with
a geometry optimized for the electronic ground state (GS), call it the
ES1//GS energy, to the ES1 energy when the ES1 geometry is optimized, call
it the ES1//ES1 energy, should allows yield energy of ES1//GS > energy of
ES1//ES1.  At least this should be true insofar as the original assertion
that CIS is a variational method is correct.

Having wrote all that I should have asked the obvious question first, did
you verify the geometry converged on a local minimum and not an
excited-state transition-state (any imaginary frequencies)?

Regards,

Phil Matz

-----Original Message-----
From: Computational Chemistry List [mailto:[email-masked]]On
Behalf Of Demetrio Antonio da Silva Filho
Sent: Tuesday, December 11, 2001 3:19 PM
To: [email-masked]
Subject: CCL:CI-Singles - Wrong Excited State Energies?

Dear CCL'ers,

I am using CI-Singles (in gaussian'98) to optimize the geometry of the first
singlet and triplet excited state.

After getting the energies of those states, I subtracted those numbers from
the
ground state energy and then compared with the excited state energies
obtained
by running a CI-S calculation  using the ground state geometry.

To my surprise, I found that the first excited state energy, obtained using
the ground
state geometry, is SMALLER than the energy difference between the first
excited state
and the ground state energies.

It means that when I optimize the geometry of the excited state using
CI-Singles, I arrive
at a geometry which energy is HIGHER than the one obtained using the ground
state geometry
-- the one that I used to begin the CI-S calculation.

Does anybody have any idea of why I get these strange results? Those
results mean that CI-Singles is not a reliable methodology to optimize
excited state geometries?

Thanks in advance,

Demetrio Filho

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---

From: "catchcaf" <[email-masked]>
Date: Tue, 11 Dec 2001 19:04:24 -0700

hello:
    My first question is how large are the differences bewteen the CIS
energies
at equilibrium geometry and excited geometry? We must keep in mind that HF
energies are only good to 0.001 hartree at best usually.
    Also, what method are you using for the ground state energy? If you are
using HF for the ground state and CIS for excited states, then this is not a
good comparison to begin with.
    Assuming you are using CIS for the ground state energy, excited states
usually
have more complicated wave functions are and harder to describe in a finite
basis. A ground state energy computed at CIS with a certain basis will be
more accurate than an excited state energy with the same basis.
    The best idea for accurate energy differences is to find the *most*
accurate wave function you can possibly find for each state and then take
differences.

mauricio cafiero
U of A
Dept. of Chem.

----- Original Message -----
From: Demetrio Antonio da Silva Filho <[email-masked]>
To: <[email-masked]>
Sent: Tuesday, December 11, 2001 4:19 PM
Subject: CCL:CI-Singles - Wrong Excited State Energies?

> After getting the energies of those states, I subtracted those numbers
> from the
obtained

---

From: Arvydas Tamulis <[email-masked]>
Date: Wed, 12 Dec 2001 13:13:10 +0200 (EET)

Dear Demetrio Antonio da Silva Filho,

CIS method is not correct for estimation of excitation energy because of
very simplyfied theory.
During your mentioned optimization of geometry in excited states using G98
HF-CIS I received your mentioned problems two years ago and additionally
sometimes SCF did not reached at all in this optimization process. Seems exist
some bugs in G98 CIS not allowing properly optimize the geometry. Try to ask
G98 responsible persons.

Presently we successfuly optimizing geometry in excited states using
GAMESS-US package.

 Best wishes, Arvydas Tamulis
*******************************************************************
                  Arvydas Tamulis

Doctor of Natural Sciences, senior research fellow

Institute of Theoretical Physics and Astronomy, Vilnius University,
Theoretical Molecular Electronics Research Group,
A. Gostauto 12, Vilnius 2600, Lithuania
e-mail: [email-masked]; WEBsite: http://www.itpa.lt/~tamulis/
fax: +(370-2)-225361  or  +(370-2)-224694
Phone: +(370-2)-620861
Home address: Didlaukio 27-40, Vilnius 2057, Lithuania
Phone: +370-9919397
*******************************************************************

On Tue, 11 Dec 2001, Demetrio Antonio da Silva Filho wrote:

> After getting the energies of those states, I subtracted those numbers from the
> ground state energy and then compared with the excited state energies obtained

---

From: "catchcaf" <[email-masked]>
Date: Wed, 12 Dec 2001 09:25:12 -0700

Hello:
    You are right, for CI with only singles, CIS ground state is equilvalent
to HF,
as the single excitations do not mix with the ground state.
    Excuse me for this error. I was thinking CI in general, and not
specifically CIS.

    By the way, in answer to the original question, no, I do not believe CIS
is a great way to model excited states, but it is a decent cheap way.

----- Original Message -----
From: Christoph van Wüllen <[email-masked]>
To: catchcaf <[email-masked]>
Sent: Wednesday, December 12, 2001 5:23 AM
Subject: Re: CCL:CI-Singles - Wrong Excited State Energies?

>     Assuming you are using CIS for the ground state energy, excited states
Is there any difference between Hartree-Fock and CIS for ground state
energies?

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---

From: "Phillip Matz" <[email-masked]>
Date: Wed, 12 Dec 2001 09:05:33 -0800

mauricio cafiero,

Please clarify, to the best of my knowledge CIS does not lower the ground
state energy.  To reduce the ground state energy you must expand the CI
treatment to include at least doubles (CISD).

Regards,

Phil Matz

-----Original Message-----
From: Computational Chemistry List [mailto:[email-masked]]On
Behalf Of catchcaf
Sent: Tuesday, December 11, 2001 6:04 PM
To: [email-masked]; Demetrio Antonio da Silva Filho
Subject: CCL:CI-Singles - Wrong Excited State Energies?

hello:

mauricio cafiero
U of A
Dept. of Chem.

----- Original Message -----
From: Demetrio Antonio da Silva Filho <[email-masked]>
To: <[email-masked]>
Sent: Tuesday, December 11, 2001 4:19 PM
Subject: CCL:CI-Singles - Wrong Excited State Energies?

obtained