52.9 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.

RMS1D=value
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.
ITMAX1D=n
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.

memory,20,m
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
rhf

label4
{surf,start1D=label1
 vmult,start2D=label1,start3D=label2,multi=4
 repar}
vscf
vci



molpro@molpro.net 2018-09-24