Keywords for Module UFF

One has to specify only the cartesian coordinates (data group $coord) to start a uff run. The program uff requires the data groups $uff, $ufftopology, $uffgradient and $uffhessian. If these keywords do not exist in the control file the program will generate these data groups.

The data group $uff contains the parameters described below. The default values--in the control file--are:

              1         1          0 ! maxcycle,modus,nqeq
         111111                      ! iterm
       0.10D-07  0.10D-04            ! econv,gconv
           0.00  1.10                ! qtot,dfac
       0.10D+03  0.10D-04       0.30 ! epssteep,epssearch,dqmax
             25      0.10       0.00 ! mxls,dhls,ahls
           1.00      0.00       0.00 ! alpha,beta,gamma
              F         F          F ! transform,lnumhess,lmd

The explanation of the variables are as follows:

maxcycle

number of max. optimization cycles (maxcycle=1: single-point calculation).

modus

can have the values +1 or -1. If modus = -1 only the topology will be calculated.

nqeq

each nqeq cycle the partial charges will be calculated. If nqeq = 0, then the partial charges are calculated only in the first cycle, if the file ufftopology does not exist.

iterm

switch for the different types of force field terms:

100000

bond terms will be calculated.

010000

angle terms will be calculated.

001000

torsion terms will be calculated.

000100

inversion terms will be calculated.

000010

non bonded van der Waals terms will be calculated.

000001

non bonded electrostatic terms will be calculated.

econv, gconv

convergence criteria for energy and gradient.

qtot

total charge of the molecule.

dfac

distance parameter to calculate the topology. If the distance between the atoms I and J is less than the sum of the covalent radii of the the atoms multiplied with dfac, then there is a bond between I and J.

epssteep

if the norm of the gradient is greater than epssteep, a deepest-descent-step will be done.

epssearch

if the norm of the gradient is smaller than epssearch, no linesearch step will be done after the Newton atep.

dqmax

max. displacement in a.u. for a coordinate in a relax step.

mxls, dhls, ahls

parameters of linesearch:

ahls

start value

dhls

increment

mxls

number of energy calculations

alpha, beta, gamma

modification parameter for the eigenvalues of the Hessian (see below): f (x) = x*(alpha + beta*exp(- gamma*x)).

transform

a switch for the transformation in the principal axis system.

lnumhess

a switch for the numerical Hessian.

lmd

a switch for a MD calculation.