Hi Peter, sorry for the wait, I had to refresh my mind on how the prefactor is calculated. Sebastian is the expert for this, so maybe he can comment of my reply.
I believe the number in tutorial scaled by a factor 5 as the post-update scale function was not working at the time when we created it. Most of the time you will have to scale the prefactor in the iteration for stabilization purposes. The manual was referring to small f, which is the "force per mass" and rho as the number density (I will clarify that in the manual later). So a more up-to-date definition see Eq. 3 of <http://dx.doi.org/10.1021/ct200706f> or Eq. 8 of <http://dx.doi.org/10.1103/PhysRevLett.108.170602>. Anyway, how is the prefactor calculated? (This now all in Gromacs units, for Espresso the prefactor will be different) F has unit kJ/mol/nm, the density calculated by csg_density has the unit u/nm^3, so the gradient of rho has unit u/nm^4 and hence the prefactor will has unit kJ nm^3/mol/u (could be simplified) rho ~ 600 u /nm^3 kappa_T = 4.5e-5 *1/bar = 7.5e-4 mol nm^3/kJ The prefactor would be m_mol/kappa_T/rho^2= 18u/(7.5e-4 mol nm^3/kJ*(600 u/nm^3)^2 = 0.067 kJ nm^3/mol/u I hope that helped. Cheers, Christoph 2013/3/6 Alexander Peyser <[email protected]>: > We've been reproducing the hybrid thermoforce coupling we've seen in a few > papers for AdRess, and we came to wonder about the thermoforce precoupling > factor. > > According to the votca documentation, eq 7.4, this is 1/(\rho^2*k_t). > The value in the tutorials in votca, the value of 0.01382 for spc. > When we've tried to calculate this value, we come up with 1.26 in internal > gromacs units, which we believe to be kJ * nm^3 * mol^-1, derived from the > pressure units of gromacs of kJ/mol/nm^3, and k_t being the compressibility > of 4.5 * 10^-5 / bar. > > Which units were used in deriving the value of 0.01382? Are we using the > correct value for k_t? > > Regards, > Alex Peyser > > -- > You received this message because you are subscribed to the Google Groups > "votca" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/votca?hl=en. > For more options, visit https://groups.google.com/groups/opt_out. > > -- Christoph Junghans Web: http://www.compphys.de -- You received this message because you are subscribed to the Google Groups "votca" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/votca?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
