In scattering or photodissociation calculations (flag BOUNDC = .false.) SPAC is the interval (sector) width in the log-derivative integration. The range from RSTART to RENDLD is divided into N steps, where

N = INT[(RENDLD - RSTART)/SPAC] + 1

Propagation is done using the Manolopoulos’s extension [D. E. Manolopoulos, J. Chem. Phys., 85, 6425 (1986)] of the original log-derivative propagator of Johnson. Typically SPAC should be on the order of 0.1 - 0.25 times the deBroglie wavelength for the system, which can be determined by the command DEBROGLI The sector width SPAC scales as the square root of the collision energy.

In bound-state calculations (flag BOUNDC = .true.), SPAC is the spacing between the equally distributed Gaussian basis

$\chi_m(R) = e^{-\alpha(R-R_m)^2}$

The scale factor is determined by means of the additional parameter C as follows:

$\alpha = \frac{c^2}{SPAC^2}$