$CONICL group (relevant if RUNTYP=CONICAL) This group governs a search for the lowest energy on the 3N-7 dimensional "seam" of intersection of two electronic potential energy surfaces of the same spin and space symmetry. Such Conical Intersections (CI) are important in photochemistry, where they serve as "funnels" for the transfer from an excited state to a lower state. See RUNTYP=MEX and the $MEX input for the simpler case where the two surfaces differ by either space or spin symmetry. Three search procedures are given, one of which requires the non-adiabatic coupling matrix element (NACME), and two others which do not require NACME information. The conical intersection search is available only for MCSCF (for which NACME are available) or for TD-DFT potential surfaces (where NACME are not available). The TD-DFT must be used in the Tamm/Dancoff approximation (see TAMMD in $TDDFT), but can be either conventional or spin-flip. The search utilizes some of the options of $STATPT, but note that the Schlegel stepper and HESS=CALC are not permitted. It may be reasonable to try the RFO stepper sometimes. The search can only be run in Cartesian coordinates. Restarts are possible only by updating the coordinates in $DATA. At present, the only solvation model that is supported is conventional TD-DFT with EFP1. OPTTYP = search procedure choice, see references below! = GPWNAC Gradient Projection with NACME, so this is only available for MCSCF. = BPUPD branching plane updating method (default) = PENALTY penalty-constrained optimization method Note that for MCSCF surfaces, if state-averaging is used, the program executes the code needed to produce NACME vectors, to producing the state-averaged gradients. There is essentially no extra time required to produce also the NACME, hence the GPWNAC stepper might as well be used. IXROOT = array of two states whose CI point is sought. For example, this might be IXROOT(1)=2,3 The roots are counted exactly the same as IROOT in the $DET or $TDDFT input groups. For the latter case, set IXROOT to 0 if you want the ground state to be one of the two surfaces searched on. There is no default for IXROOT! SYMOFF = flag to switch off point group symmetry, the default is .TRUE. DEBUG = flag to print debugging info, default is .FALSE. The following are meaningful only for OPTTYP=PENALTY: TOLSTP = energy difference tolerance default=1d-6 Hartree TOLGRD = gradient convergence tolerance default=5d-3 Hartree/Bohr ALPHA = parameter ensuring a singularity free penalty, default=0.02 Hartree SIGMA = Lagrange multiplier for the penalty term. In case the energy gap between the states is not acceptable at the CI point, increase the value. default = 3.5 (unitless) An understanding of the search procedures can be gained by reading the following papers: Gradient Projection with NACME: M.J.Bearpark, M.A.Robb, H.B.Schlegel Chem.Phys.Lett. 223, 269(1994) Branching Plane Updating method: S.Maeda, K.Ohno, K.Morokuma J.Chem.Theor Comput. 6, 1538(2010) Penalty constrained update method: B.G.Levine, C.Ko, J.Quenneville, T.J.Martinez Mol.Phys. 104, 1039(2006) B.G.Levine, J.D.Coe, T.J.Martinez J.Phys.Chem.B 112, 405(2008) A comparative study of the first two procedures is T.W.Keal, A.Koslowski, W.Thiel Theoret.Chem.Acc. 118, 837(2007) =========================================================== ===========================================================

generated on 7/7/2017