This method keyword requests an excited state calculation using the time-dependent Hartree-Fock or DFT method[Bauernschmitt96a,Casida98,Stratmann98,VanCaillie99,VanCaillie00,Furche02,Scalmani06]; analytic gradients are available in Gaussian 09[Furche02,Scalmani06]. Time-dependent DFT calculations can employ the Tamm-Dancoff approximation, via theTDAkeyword.TD-DFTBcalculations can also be performed[Trani11].
Note that the normalization criteria used is
Electronic circular dichroism (ECD) analysis is also performed during these calculations[Helgaker91,Bak93,Bak95,Olsen95,Hansen99,Autschbach02].
Singlets
Solve only for singlet excited states. Only effective for closed-shell systems, for which it is the default.
Triplets
Solve only for triplet excited states. Only effective for closed-shell systems.
50-50
Solve for half triplet and half singlet states. Only effective for closed-shell systems.
Root=N
Specifies the “state of interest”. The default is the first excited state (N=1).
NStates=M
Solve forMstates (the default is 3). If50-50is requested,NStatesgives the number of each type of state for which to solve (i.e., the default is 3 singletsand3 triplets).
Add=N
Read converged states off the checkpoint file and solve for an additionalNstates. This option impliesReadas well.
Read
Reads initial guesses for the states off the checkpoint file. Note that, unlike for SCF, an initial guess for one basis set cannot be used for a different one.
EqSolv
Whether to perform equilibrium or non-equilibrium PCM solvation.NonEqSolvis the default except for excited state optimizations and when the excited state density is requested (e.g., withDensity=CurrentorAll).
IVOGuess
Force use of IVO guess. This is the default for TD Hartree-Fock.NoIVOGuessforces the use of canonical single excitations for guess, and it is the default for TD-DFT. TheHFIVOGuessoption forces the use of Hartree-Fock IVOs for the guess, even for TD-DFT.
SOS
Do sum-over states polarizabilities, etc. By default, all excited states are solved for. A list of frequencies at which to do the sums is read in. Zero frequency is always done and need not be in the list.
Conver=N
Sets the convergence calculations to 10-Non the energy and 10-(N-2)on the wavefunction. The default isN=4 for single points andN=6 for gradients.
An energy range can be specified forCISandTDexcitation energies using the following options toCIS,TDandTDA.
GOccSt=N
Generate initial guesses using only active occupied orbitalsNand higher.
GOccEnd=N
Generate initial guesses: ifN>0, use only the firstNactive occupied orbitals; ifN<0, do not use the highest |N| occupieds.
GDEMin=N
Generate guesses having estimated excitation energies ≥N/1000 eV.
DEMin=N
Converge only states having excitation energy ≥N/1000 eV; ifN=-2, read threshold from input; ifN<-2, set the threshold to |N|/1000 Hartrees.
IFact=N
Specify factor by which the number of states updated during initial iterations is increased.
WhenReduce=M
Reduce to the desired number of states after iterationM.
The default forIFactisMax(4,g) wheregis the order of the Abelian point group. The default forWhenReduceis 1 forTDand 2 forTDAandCIS. Larger values may be needed if there are many states in the range of interest.
Energies and gradients using Hartree-Fock or a DFT method.
Here is the key part of the output from aTDexcited states calculation: