$TDDFT group (relevant if TDDFT chosen in $CONTRL) This group generates molecular excitation energies by time-dependent density functional theory computations (or time-dependent Hartree-Fock, also known as the Random Phase Approximation). The functional used for the excited states is necessarily the same one that is used for the reference state, specified by DFTTYP in $CONTRL. For conventional TD-DFT (TDDFT=EXCITE in $CONTRL), the orbitals are optimized for RHF or UHF type reference states. Analytic nuclear gradients are available for singlet excited states, while the energy of excited states of other multiplicities can be computed. Two-photon absorption cross-sections may be predicted for singlet excited states. Ground state hyperpolarizabilities may be computed with the TDDFT module. For spin-flip TD-DFT (TDDFT=SPNFLP in $CONTRL), the calculation obtains orbitals for a reference state of either UHF or ROHF type, with MULT in $CONTRL determining the Ms quantum number of the reference. The reference state's Ms is set equal to the S value implied by $CONTRL's MULT=2S+1. The SF-TD-DFT then uses only determinants with Ms=S-1, due to the flip of one alpha spin into a beta spin. This means that target states (which are spin contaminated) will have multiplicities around the range S-1 to S, only. It is quite possible for some of the target states to have a lower energy than the reference!!! Nuclear gradients and properties are available. See just below for "limitations" below regarding the two different TD-DFT types. TD-DFT is a single excitation theory. All of the caveats listed in the $CIS input group about states with double excitation character, need for Rydberg basis sets, greatly different topology of excited state surfaces, and so on apply here as well. Please read the introduction to the $CIS input group! If you use very large or very small Gaussian exponents, you may need to increase the number of radial grid points (the program prints advice in such cases). TDHF, TDDFT, and CIS are related in the following way: -- Tamm/Dancoff approximation --> | TDHF CIS DFT | V TDDFT TDDFT/TDA Here TDHF means absorption of photons, to produce excited states (TDHF is called RPA in the physics community). This meaning of TDHF should not be confused with the photon scattering processes computed by RUNTYP=TDHF or TDHFX, which generate polarizabilities. Note, in particular, that CITYP=CIS is equivalent to using TDDFT=EXCITE DFTTYP=NONE TAMMD=.TRUE., provided the former is run with no frozen cores. Solvent effects for CIS calculations are therefore available via the TDDFT codes. Excited state properties are calculated using the TDDFT excited state electronic density only during gradient runs, or by setting TDPRP below. The TD-DFT codes excite all electrons, that is, there is no frozen core concept. Please see the 4th chapter of this manual for more information on both types of TD-DFT. "limitations" for TDDFT=EXCITE: Permissible values for DFTTYP are shown below. These include "NONE" which uses TDHF (i.e. the Random Phase Approximation), noting that extra states may need to be solved for in order to be sure of getting the first few states correctly. If nuclear gradients are needed, you may choose any of the following functionals: NONE SVWN, SOP, SLYP, OLYP, BVWN, BOP, BLYP (and their LC=.TRUE. versions) B3LYP, CAMB3LYP, B3LYPV1R, PBE, PBE0 For evaluation of just the excitation energies, you may use many more functionals, notably including the metaGGAs in the last three lines: NONE SVWN, SVWN1, SPZ81, SP86, SOP, SLYP, BVWN, BVWN1, BPZ81, BP86, BOP, BLYP, OLYP, B3LYP, CAMB3LYP, B3LYPV1R, B3PW91, X3LYP, PW91, PBE, PBE0, VS98, PKZB, M05, M05-2X, M06, M06-HF, M06-L, M06-2X, M08-HX, M08-SO TPSS, TPSSm, TPSSh, and revTPSS The LC flag in $DFT automatically carries over to TDDFT runs. The LC option may be used with the "B" functionals, and (like the similar range-separated CAMB3LYP) is useful in obtaining better descriptions for charge-transfer excitations or Rydberg excitation energies than are the conventional exchange correlation functionals (whether pure or hybrid). The LC flag is also available for excited state gradient computation. Limits specific to the references for TDDFT=EXCITE are: For SCFTYP=RHF, excitation energies can be found for singlet or triplet coupled excited states. For singlet excited states only, analytic gradients and properties can be found, for either full TD-DFT or in the Tamm/Dancoff approximation. For RHF references, solvent effects can be included by EFP1 or PCM (or both together), for both TD-DFT excitation energies and their nuclear gradients. DFTB (possibly combined with PCM) may be chosen as well, and analytic gradients for singlet and triplet are available. For SCFTYP=UHF, excited states with the same spin projection as the ground state are found. MULT in $CONTRL governs the number of alpha and beta electrons, hence Ms=(MULT-1)/2 is the only good quantum number for either the ground or excited states. Since U-TDDFT is a single excitation theory, excited states with <S> values near Ms and near Ms+1 will appear in the calculation. There are no properties other than the excitation energy, nor gradients, nor solvent effects, at present. "limitations" for TDDFT=SPNFLP: Spin-flip TDDFT is programmed in the "collinear approximation" which means only the HF exchange term carries a large impact on the excitation energies. Pure DFT functionals may be used, but normally hybrids with large HF exchange fractions are used. The LC option for range-separation hybrids cannot be used, which also removes CAMB3LYP. Finally, no meta-GGA may be used. Note that spin-flip TD-DFT in the Tamm/Dancoff approximation using DFTTYP=NONE is equivalent to spin-flip CIS. MULT below is ignored, as the Ms of target states is fixed solely by MULT in $CONTRL. The spin-flip code operates only in the Tamm/Dancoff approximation, so TAMMD below is automatically .TRUE. Nuclear gradients and/or excited state properties are available only in the gas phase. Solvation effects are available for both energy and gradient calculations, for EFP1, C-PCM, or both. --------- NSTATE = Number of states to be found (excluding the reference state). The default is 1 more state. IROOT = State used for geometry optimization and property evaluation. (default=1) TDDFT=EXCITE counts the reference as 0, and this should be the lowest state. Hence IROOT=1 means the 1st excited state, just as you might guess. TDDFT=SPNFLP labels the reference state as 0, but this might not be the lowest state overall. The meaning of IROOT=1 is the lowest state, omitting the reference state from consideration. Hence IROOT=1 might specify the ground state! MULT = Multiplicity (1 or 3) of the singly excited states. This keyword applies only when the reference is a closed shell. (default is 1) This parameter is ignored when TDDFT=SPNFLP. TDPRP = a flag to request property computation for the state IROOT. Properties can only be obtained when the nuclear gradient is computable, see gradient restrictions noted in the introduction to this group. Properties require significant extra computer time, compared to the excitation energy alone, so the default is .FALSE. Properties are always evaluated during nuclear gradient runs, when they are a free by-product. TPA = a flag requesting two-photon absorption cross- sections. These are computed for each of the NSTATE excited states, after first evaluating their excitation energies. The TPA calculation is only available for closed shell references, only for singlet excited states (MULT=1), and may not be used with the Tamm/Dancoff approximation. Solvent effects may be treated by EFP. TAMMD is a flag selecting the Tamm/Dancoff approximation be used. This may be used with closed shell excitation energies or gradients, or open shell excitation energies. Default = .FALSE. This parameter is ignored by TDDFT=SPNFLP, which is only coded in the Tamm/Dancoff approximation. NONEQ is a flag controlling PCM's solvent behavior: .TRUE. splits the dielectric constant into a bulk value (EPS in $PCM) and a fast component (EPSINF), see Cossi and Barone, 2001. The idea is that NONEQ=.t. is appropriate for vertical excitations, and .f. for adiabatic. (the default is .TRUE.) This keyword is ignored by TDDFT=SPNFLP. * * * ground state polarizability calculation * * * (use TDDFT=HPOL option in $CONTRL) These two frequency dependent polarizability calculations may be requested in the same run (more efficient). These properties are available only for closed shell references, require the default MULT=1 value in this input group, and may not be used with the Tamm/Dancoff approximation. Solvent effects may be treated by EFP. ALPHA = requests the polarizability. Default=.FALSE. If BETA is not chosen, give just one PFREQ. BETA = requests the hyperpolarizability. Default=.FALSE. Two values are required for PFREQ. PFREQ = an array of one or two input frequencies, omega1 and omega2, to yield the polarizability alpha(omega1;omega1) [if BETA=.F.] alpha(omega2;omega2) [if BETA=.T.] alpha(omega3;omega3) [if BETA=.T.] and/or to yield the hyperpolarizability beta(omega3;omega1,omega2). The output photon frequency is determined from omega3=-(omega1+omega2). Useful special cases second harmonic generation beta(-2W;W,W), electro-optic Pockels effect beta(-W;W,0), and optical rectification beta(0;W,-W) are among the possibilities. The default is the static polarizability and/or static hyperpolarizability: PFREQ(1)=0.0,0.0 PFREQ is given in atomic units: PFREQ=45.56/lamda, for wavelength lambda in nm. * * * Grid Selection * * * The grid type and point density used in $TDDFT may be chosen independently of the values in $DFT. Excitation energies accurate to 0.01 eV may be obtained with grids that are much sparser than those needed for the ground state, and this is reflected in the defaults. Prior to April 2008, the default grid was NRAD=24 NTHE=8 NPHI=16. NRAD = number of radial grid points in Euler-Maclaurin quadrature, used in calculations of the second or third derivatives of density functionals. (default=48) NLEB = number of angular points in the Lebedev grid. (default=110) NTHE = number of theta grid points if a polar coordinate grid is used. NPHI = number of phi grid points if a polar coordinate grid is used. NPHI should be twice NTHE. SG1 = flag selecting "standard grid one". (default=.FALSE.) See both $DFT and REFS.DOC for more information on grids. The "army grade" standard for $TDDFT is NRAD=96 combined with either NLEB=302 or NTHE=12/NPHI=24. the remaining parameters are technical in nature: CNVTOL = convergence tolerance in the iterative TD-DFT step. (default=1.0E-7) MAXVEC = the maximum number of expansion vectors used by the solver's iterations, per state (default=50). The total size of the expansion space will be NSTATE*MAXVEC. NTRIAL = the number of initial expansion vectors used. (default is the larger of 5 and NSTATE). ========================================================== ==========================================================

generated on 7/7/2017