2016-06-14 12:30 GMT+02:00 Jyotirmoy Deb <[email protected]>:
> Dear SIESTA users, > I want to do Van der waals dispersion correction using SIESTA. I have used > a dispersion potential of Grimme type as suggested in Grimme's paper (J. > Comput. Chem. Vol 27, 1787-1799 (2006)). My system is a carbon nanotube and > nitrogen molecule is confined within it. I have prepared the input as given > below. > %block MM.Potentials > 1 1 Grimme 60.710 5.488 carbon carbon > 1 2 Grimme 60.710 5.384 carbon nitrogen > %endblock MM.Potentials > > MM.Grimme.D 20.0 > MM.Grimme.S6 1.66 > MM.Cutoff 30. Bohr > Now my queries are: > (1). Whether I have to consider the interaction between nitrogen-nitrogen > and nitrogen-carbon also? > If there is only one nitrogen atom, then no. Also, carbon-nitrogen == nitrogen-carbon. So no need to specify both. > (2). Should I use the original Grimme parameter value as given in the > paper or I have to multiply it by 34.69142857 as mentioned in siesta-l? > This is always extremely tricky, I always forget what to do. However, if you download the latest trunk version (on launchpad) there is now a utility called fdf2grimme (in Util/Grimme) You call this by: $> fdf2grimme RUN.fdf and it will spit out the required information (with all quantities correctly specified). Remark I have not checked all things, but I think they are all correct :) > (3). If I substitute one carbon atom in the nanotube by any impurity atom > then what are the interactions between the atoms (carbon, nitrogen, > impurity atom) that I have to consider? > Essentially this method has nearly no overhead, so you may easily add all interactions. However, the Grimme method is based on a potential with a certain distance range. You may check the potential after running the siesta calculation and plot the MM.pot* files which describe the different potentials according to the atomic center distances. -- Kind regards Nick
