Geometry optimization: *WALK

 

Directives controlling one of the two second-order geometry  optimizations as well as the execution of dynamical walks and numerical differentiation  in calculations of Raman intensities and optical activity   , appear in the *WALK   section.

.DISPLA  

READ (LUCMD, *) DISPLC

Displacement taken in a numerical differentiation . This applies both for a numerical molecular Hessian , as well as in calculation of Raman intensities and optical activity   . Read one more line specifying value (*). Default is 10 a.u. However, note that this variable do not determine the displacements used when evaluating numerical gradient for use in first-order geometry optimizations with MP2 or CI wave functions    , which is controled by the .DISPLA   keyword in the *MINIMI   module.

.DYNAMI  

Perform a ``dynamic walk'' : integrate the classical equations of motion  for the nuclei analytically on a locally quadratic surface. The method is discussed in Ref. [12] as well as in Section .

.EIGEN  

Take a step to the boundary of the trust region  along the eigenvector mode  specified by .MODE  .

.FRAGME  

READ (LUCMD, *) NIP
READ (LUCMD, *) (IPART(IP), IP = 1, NIP)

Identify which fragments  atoms belong to in a dynamic walk. Read one more line specifying the number of atoms (the total number of atoms in the molecule), then one more line identifying which fragment an atom belongs to. The atoms in the molecule are given a number, different for each fragment. See also the discussion in Sec. .

.GRDEXT  

Perform a gradient extremal-based  optimization. The algorithm used in this kind of optimization is thoroughly described in Ref.[10]. This is default walk type if the index of the critical point searched is higher than 1. See also the discussion in Sec. .

.HARMON  

READ (LUCMD, *) ANHFAC

Threshold for harmonic dominance. Read one more line specifying value. Default is 100. This is another way of changing the criterion for changes of the trust radius . See also the keyword .TRUST  .

.IMAGE  

Locate a transition state  using a trust-region-based image surface  minimization. Note that only a point with a Hessian index of 1 can currently be located with this method, not higher-order stationary points. See also the discussion in Sec. .

.INDEX  

READ (LUCMD,*) IWKIND

Desired Hessian index  (strictly, of the totally symmetric block of the Hessian) at the optimized geometry. Read one more line specifying value. Default is 0 (minimum). Note that a stationary point with the wrong Hessian index will not be accepted as an optimized geometry.

.IRC  

READ (LUCMD, *) IRCSGN

Set the geometry walk to be an Intrinsic Reaction Coordinate (IRC)   as described in Ref. [18, 19]. Read one more line containing the sign (-1 or 1) of the reaction coordinate. It cannot be decided in advance which reaction pathway a specific sign is associated with. See also the discussion in Sec. .

.ISOTOP  

READ (LUCMD, *) NIS
READ (LUCMD, *) (ISOTPS(IS), IS = 1, NIS)

Specify the isotopic constitution  of the molecule under investigation. This is most interesting in dynamic walks , as well as when using mass-scaled atomic coordinates . Note that the internal structure of ABACUS  uses Cartesian coordinates, and for vibrational analysis alone the keyword .ISOTOP   in the *VIBANA   input section is to be preferred. Note also that for defining center of mass coordinates, there is a similar ISOTOP keyword in the general input module, and this will become the only keyword for specifying isotopic substitutions in later versions of the program. The .ISOTOP   keyword in this input module (*WALK  ) is to become obsolete.

.KEEPSY  

Ensure that the symmetry of the molecule is not broken. The threshold for determining a mode as breaking symmetry is controled by the keyword .ZERGRD  .

.MASSES  

Mass-scale the atomic coordinates . This is the default for dynamic walks , gradient extremal  walks and in calculations of Intrinsic Reaction Coordinates (IRCs)  .

.MAXNUC  

READ (LUCMD, *) XMXNUC

Maximum displacement  allowed for any one atom as a result of the geometry update. Read one more line specifying value. Default is 0.5.

.MAXTRU  

READ (LUCMD, *) TRUMX1

Set the maximum arc length in an Intrinsic Reaction Coordinate (IRC) walk  . Read one more line containing the maximum arc length. Default is 0.10. Note that this arc length is also affected by the .TRUST   keyword, and if both are specified, the arc length will be set to the minimum value of these to.

.MODE  

READ (LUCMD,*) IMODE

Mode to follow in level-shifted Newton optimizations for transition states . Read one more line specifying mode. Default is to follow the lowest mode (mode 1).

.MODFOL  

Perform a mode-following (level-shifted Newton) optimization. This is the default for minimizations and localization of transition states. See also discussion in Section .

.MOMENT  

READ (LUCMD, *) NSTMOM
DO 265 IP = 1, NSTMOM
READ (LUCMD, *) ISTMOM(IP), STRMOM(IP)
265 CONTINUE

Initial momentum for a dynamic walk  . Read one more line specifying the number of modes to which there is added an initial momentum. Then read one line for each of these modes, containing first the number of the mode, and then the momentum. The default is to have no momentum. See also the section describing how to perform a dynamic walk, Sec. .

.NATCON  

Use the natural connection  when orthogonalizing the predicted molecular orbitals at the new geometry. By default the symmetric connection is used.

.NEWTON  

Use a strict Newton-Raphson  step to update the geometry. This means that no trust region will be used.

.NOGRAD  

READ (LUCMD, *) NZEROG
READ (LUCMD, *) (IZEROG(I), I = 1, NZEROG)

Set some gradient elements to zero. Read one more line specifying how many elements to zero, then one or more lines listing their sequence numbers.

.NOORTH  

The predicted molecular orbitals at the new geometry are not orthogonalized. Default is that the orbitals are orthogonalized with the symmetric connection. Orthogonalization can also be done with the natural connection [34]. See the keyword .NATCON  .

.NOPRED  

No prediction of the energy of the wave function at updated geometry.

.NUMERI  

Do a numerical differentiation , for instance when calculating Raman intensities or Raman optical activity, see Sections  and .

.PRINT  

READ (LUCMD,*) IPRWLK

Set the print level in the prediction of new geometry steps. Read one more line containing print level. Default value is the value of IPRDEF in the general input module.

.RATLIM  

READ (LUCMD, *) RTMIN, RTRGOD, REJMIN, REJMAX

Limits on ratios between predicted and observed energy change. Read one more line specifying four values (*). These are respectively the bad prediction ratio, good prediction ratio, low rejection ratio and high rejection ratio. Defaults are 0.4, 0.8, 0.1, and 1.9.

.REJECT  

Signals that the previous geometry step was rejected , and the trust region  is reduced. This keyword is used in case of restarts to tell the program that when the program stopped, the last geometry was in fact rejected.

.REPS  

READ (LUCMD, *) NREPS
READ (LUCMD, *) (IDOREP(I), I = 1, NREPS)

Consider perturbations of selected symmetries only. Read one more line specifying how many symmetries, then one line listing the desired symmetries. Note that only those symmetries previously defined to be true with the keyword .REPS   from the ABACUS  input modules will be calculated. This keyword thus represents a subset of the .REPS   of the general input module.

.SCALE  

READ (LUCMD, *) NUMNUC
DO 7000 INUC = 1, NUMNUC
READ (LUCMD, *) IATOM,(SCALCO(J,IATOM), J = 1, 3)
7000 CONTINUE

Scale the atomic coordinates. Read one more line specifying how many atoms to scale, then one line for each of these atoms (*) specifying the atom number and scale factors for all three Cartesian coordinates. Default is no scaling of the atomic coordinates.

.RESTART  

Tells the program that this is a restarted geometry optimization  and that information may therefore be available on the DALTON.WLK file.

.STRICT  

Strict mode following. Obsolete keyword. Do not use.

.TOLERA  

READ (LUCMD, *) TOLST

Threshold for convergence of the geometry optimization (on gradient norm). Read one more line specifying the threshold (*). Default is 10 .

.TRUST  

READ (LUCMD, *) TRUSTR, TRUSTI, TRUSTD

Trust region information . Read one more line specifying three values (*): initial trust radius, factor by which radius can be incremented, and factor by which it can be decremented. Defaults are 0.5, 1.2 and 0.7, respectively; initial trust radius default is 0.3 if desired Hessian index is greater than zero. In dynamic walks  the trust radius is by default put to 0.005, and in walks along an Intrinsic Reaction Coordinate (IRC)   the default trust radius is 0.020. For dynamical walks the default increment and decrement factor is changed to 2.0 and 0.8 respectively.

.ZERGRD  

READ (LUCMD, *) ZERGRD

Threshold below which gradient elements are treated as zero. Read one more line specifying value (*). Default is 10 . This keyword is mainly used for judging which modes are symmetry breaking when using the keyword .KEEPSY   as well as when deciding what step to take when starting a walk from a transition state.