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.

.ANHARM

Requests that a determination of the cubic force field is to be determined. By default this is done calculating numerical derivatives of analytical Hessians in Cartesian coordinates.

.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$^{-4}$ 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 controlled by the .DISPLA keyword in the *OPTIMIZE 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. [28] as well as in Section 7.2.2.

.ECKART

DO I = 1, NUCDEP
READ (LUCMD,'(7X,F17.10,2F24.10)')
& (ECKGEO(J,I), J = 1, 3)
END DO

During a vibrational averaging, ensure that the properties are transformed to the appropriate Eckart axis system. The coordinate system given should be that of the equilibrium geometry of the molecule. The coordinates should be given in bohr, and should be given for all symmetry generated atoms in the order given in the input.

.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. 7.2.2.

.GRDEXT

Perform a gradient extremal-based optimization. The algorithm used in this kind of optimization is thoroughly described in Ref.[25]. This is the default walk type if the index of the critical point searched is higher than 1. See also the discussion in Sec. 7.1.4.

.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. 7.1.2.

.INDEX

READ (LUCMD,*) IWKIND

Desired Hessian index (strictly speaking, 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. [37]. 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. 7.2.1.

.KEEPSY

Ensure that the symmetry of the molecule is not broken. The threshold for determining a mode as breaking symmetry is controlled 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 7.1.5.

.MOMENT

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

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. 7.2.2.

.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.

.NO CENTRIFUGAL FORCES

Do not include contributions from centrifugal forces when calculating vibrationally averaged geometries at a finite temperature.

.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 [64]. See the keyword .NATCON.

.NOPRED

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

.NORMAL

Do the calculation of effective (vibrationally averaged) geometries in normal coordinates. This will restrict the calculation of the effective geometry to one isotopic species (by default the most abundant one).

.NUMERI

Do a numerical differentiation, for instance when calculating Raman intensities or Raman optical activity, see Sections 8.4 and 11.4.

.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, *) RTRMIN, 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 was 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.

.RESTART

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

.REUSE

Use the property derivatives available on the file DALTON.WLK in a calculation of the harmonic contribution to the vibrational average. In this case, only a new force field will be calculated.

.SCALE

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

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.

.TEMPERATURES

READ (LUCMD, *) NTEMP
READ (LUCMD, *) (TEMP(ITMP), ITMP=1,NTEMP)

Read a set of temperatures for which the effective (rovibrationally averaged) geometries are to be calculated. Read one more line containing the number of different temperatures, and another line containing the list of temperatures.

.TOLERANCE

READ (LUCMD, *) TOLST

Threshold for convergence of the geometry optimization (on gradient norm). Read one more line specifying the threshold (*). Default is 10$^{-5}$.

.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 0.02. For dynamical walks the default increment and decrement factor is changed to 2.0 and 0.8 respectively.

.VIBAVE

Request the calculation of the harmonic contribution to the vibrational average of a molecular property.

.ZERGRD

READ (LUCMD, *) ZERGRD

Threshold below which gradient elements are treated as zero. Read one more line specifying value (*). Default is 10$^{-5}$. 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.