MOLPRO

47 POTENTIAL ENERGY SURFACES (SURF) 359
MODE=n
Denotes the normal coordinate to be scaled.
SFAC=value Scaling factor for mode MODE. The default is 1.0.
47.6 Modeling of high-order n-body terms
REPAR,options
Within the framework of multi-level calculations (see the directive VMULT), 3D and 4D terms
can be modeled. The modeling scheme is based on a reparametrization of the semiempirical
AM1 method. Consequently, in the input stream the energy variable to be read in must refer
to a semiempirical calculation. After the 2D terms the program optimizes the semiempirical
parameters in order to represent the 1D and 2D surfaces best.
TYPE=n
RMS1D=n
ITMAX1D=n
TYPE=1 specifies a standard reparametrization solely based on a local
optimization starting from standard semiempirical parameters. TYPE=2
invokes a global optimization prior to the local one.
The keywords RMS1D and RMS2D specify the threshold for terminating
the 1D and 2D iterations in the local optimization of the semiempirical
parameters. The defaults are given by RMS1D=1.d-6 and RMS2D=1.d-
6.
The maximum number of iterations in the local optimization of the
semiempirical parameters can be controlled by ITMAX1D and ITMAX2D.
The defaults are ITMAX1D=100 and ITMAX2D=150.
The following example shows the input for a surface calculation in which the 3D terms will be
modeled without the use of global optimization schemes.
memory,20,m
geomtyp=xyz
orient,mass
geometry={
3
Water
O 0.0675762564 0.0000000000 -1.3259214590
H -0.4362118830 -0.7612267436 -1.7014971211
H -0.4362118830 0.7612267436 -1.7014971211
}
hf
mp2
optg
freq
label1
abinitio
basis=vdz
int
rhf
mp2
goto,label4
label2
semi,am1
int