- From: Ulrike Salzner <salzner^at^fen.bilkent.edu.tr>
- Organization: Bilkent University
- Subject: CCL: TDHF
- Date: Wed, 25 Jun 2003 12:02:57 +0300
Many thanks to Stefan Grimme, Artem Masumov, and Doug Fox.
I asked whether it is possible to calculate and optimize the ground state
of a system with TDHF. The answer is no. Like CIS, TDHF does not provide
a correction to the ground state energy. More important I was warned that
the TDHF geometry optimization for excited states in G98 is an approximation
and should not be used. The option has been removed in G03.
One comment of mine to the statement that TDDFT is superior to TDHF: I am
aware that TDDFT is quite successful in general. Unfortunately, the only
excited state that is currently of interest to me (the 1Bu excited state
of polyenes) is not well reproduced, especially with increasing size and
conjugation length, which is exactly what I need to investigate. TDHF, in
contrast, gives numbers similar to CASMP2. Therefore, it is bad news indeed
that the geometries can not be optimized at this level of theory.
The original question and the answers follow below:
the time-dependent Hartree-Fock
method is described as a method for
calculating excited states. I would
like to know whether one can also
optimize the ground state including
correlation with TDHF. In other
words, if I use the keywords "fopt"
and "nroot=0" in Gaussian what am I
calculating? I know that CIS does not
make a correction to the ground
state because of Brillouin's theorem
but I am not sure what TDHF
includes exactly. The reason why I
am considering this is that I would
like to compare the excitet state and
the ground state geometries on
equal footing. Would it be better to
compare the excited state TDHF
geometry to the HF ground state
Thanks in advance,
in fact TDHF is not defined for the ground state but there is a close
analogy between CIS and TDHF (expanded in singles only,
CIS equations can be derived from the non-Hermitian TDHF
problem by neglecting the so-called B-matrix).
>From that I would argue that the ground state analogue of TDHF is just HF.
Prof. Dr. Stefan Grimme
Organisch-Chemisches Institut (Abt. Theoretische Chemie)
Westfaelische Wilhelms-Universitaet, Corrensstrasse 40
D-48149 Muenster, Tel (+49)-251-83 36512/33241/36515(Fax)
Just like CIS, TDHF does not improve the ground state.
So correct comparison would be TDHF optimized excited state and HF
optimized ground state.
In fact, TDHF only differs from CIS in that it has nonzero V-O block in
hamiltonian (and thus, in transition density) matrix.
In g98 this block is missing from the routine evaluating gradients, so
excited state optimization with analytical gradients gives incorrect
(approximate) results. That is why in g03 this option is blocked. In
Turbomol TDHF opt. is coded fine.
To optimize the excited state at TDHF level you need to do Opt=Numer,
which is much slower.
Please keep in mind that TDHF is inferior to TDDFT at the same
Hope this helps,
__ ___________ Artem.Masunov^at^LANL.gov
/ \ / __ __ \ www.t12.lanl.gov/home/amasunov
/ \/\ \ \ \ \ \ 505.665.2635, Fax:505.665.3909
/ /\ \ \ \ \ \ \ \ Theoretical Division, MS B268
/ ____ \ \ \ \ \ \ \ Los Alamos National Lab
/__/\ _/\ _\ \ _\ \ _\ \ _\ Los Alamos NM 87545
\ _\/ \/__/\ __/\ __/\ __/ ____________________________
G98/03 does not have gradients implement analytic gradients for
TDHF or TDDFT so optimizations need to be performed with only
energy values OPT=(EF,EnOnly) and a symbolic Z-matrix. But it
can be done for medium to small systems. Or at least a few degrees
The TDHF and CIS methods both use the HF solution as the reference
and neither of them improve on the ground state description.
In the sense that neither the Excited state or the Ground state
is really correlated it has been our experience that structures in
CIS are similar in quality to HF although often a slightly larger basis
is needed. To go beyond this you might want to consider SACCI
which is in G03 or CASSCF, both of which can include correlation,
dynamic vs. static, and treat ground and excited state on a equal