Description
SM2.1 is no longer available and
SM5.2,
SM5.2R,
SM5C, or
SM5CR
should be used instead.
This keyword activates the SM2.1 AMSOL solvation model and the force trapezoid radial
quadrature scheme contributed by C. J. Cramer, G. D. Hawkins, G. C. Lynch, D. G. Truhlar, and
D. A. Liotard. (See Chapter 15, AMSOL Model Module for a more complete
description of the AMSOL methods and additional dedicated keywords. All other SMx models use
the force rectangle scheme for radial quadratures, resulting in slightly less accurate
evaluations of these quantities and slower speed.) The keyword SM2.1 together with the AM1
keyword requests a calculation in aqueous solution by the AM1-SM2.1 method. This is completely
analogous to the SM2 method except that it was parameterized using essentially converged
radial quadratures in the dielectric screening algorithm, as calculated by the force trapezoid
rule, whereas in SM2 the parameters were obtained using unconverged quadratures carried out by
the force rectangle rule. The force trapezoid rule is more efficient and more stable than the
force rectangle rule, and it is recommended for that reason. Except for small changes in the
parameters and the use of a different radial quadrature scheme, the SM2.1 model is the same as
SM2, and the results are generally very similar. The force trapezoid quadrature scheme,
however, allows use of the TEXPN, TONE, and EXTM options, which are unavailable in SM1, SM1a,
SM2, and SM3. Greater computational efficiency of the force trapezoid rule and/or the use of
one or more of the TEXPN, TONE, and EXTM keywords are the main reasons why the SM2.1 option
would be chosen over one of the previous models.
