Multipole moments with cutoffs

[kratman]

I am not sure if this is a bug or if I am attempting to use TINKER incorrectly, but I would like to use the "taper" and "cutoff" keywords with AMOEBA. The taper keywords do not seem to have an effect on multipolar force fields, although the manual seems to suggest that taper is implemented for multipoles. I tried the calculations with both the static binaries on the TINKER website and source code compiled from GitHub.

As a test system I calculated the energy of NaCl at different bond distances. Using the AMBER99 force field, cutoff/taper smoothly adjusted the energy. With AMOEBA09, all settings gave the same result as using AMBER99 with the truncate keyword. Some of the input and output (energies at distances between 0 an 20 angstroms) are listed below.

Taper keyword file:

parameters NaCl09.prm
#parameters NaCl99.prm
cutoff 20.0
mpole-cutoff 20.0
taper 0.5
mpole-taper 0.5
#truncate
vdwterm none

AMBER99 taper:

1 A -13.439203229605 eV
4 A -2.6398434916303 eV
8 A -0.8399502020400 eV
12 A -0.2447941578734 eV
16 A -0.0333936331889 eV
20 A 0.00000000000000 eV

AMBER99 truncate:

1 A -14.399146317589 eV
4 A -3.5997865791806 eV
8 A -1.7998932895903 eV
12 A -1.1999288598714 eV
16 A -0.8999466447951 eV
20 A -0.7199573156626 eV

AMOEBA09 taper:

1 A -14.399644861664 eV
4 A -3.5999112154161 eV
8 A -1.7999556077080 eV
12 A -1.1999704052832 eV
16 A -0.8999778040708 eV
20 A -0.7199822430832 eV

Thanks,
-kratz