RE: [ESPResSo-devel] shifts

[Limbach, Hans Joerg, LAUSANNE, NRC-FS]

Hi,

The implementation (which in this case at least is consistent with the
documentation) is
frac = lj_sigma / (r_ij - lj_offset )
E_LJ = 4*lj_eps*( frac^12 - frac^6 + shift   ) 

In other words the shift has to be
fcut = lj_sigma / ( lj_cut - lj_offset )
shift = - ( fcut^12 - fcut^6 )

I have added a procedure to ABHmath.tcl which does exactly this:
calc_lj_shift <lj_sigma> <lj_cutoff> <lj_offset>
(And I also added the documentation in the user guide ;-) )

It's probably good to use that in all scripts (Axel you can hear me?)
Hanjo

> -----Original Message-----
> From: address@hidden 
> [mailto:address@hidden On 
> Behalf Of Axel Arnold
> Sent: mardi, 9. octobre 2007 13:42
> To: ESPResSo developers' mailing list
> Subject: [ESPResSo-devel] shifts
> 
> Hi all,
> 
> Peter Kosovan has a point: this is the current state of 
> shifting in our sample
> scripts:
> espresso_logo.tcl:set lj1_shift   $lj1_eps
> kremerGrest.tcl:set lj1_shift   0.25
> lj_liquid.tcl:set lj1_shift   $lj1_eps
> maggs.tcl:set lj1_shift   [expr 0.25*$lj1_eps]
> pe_network.tcl:set LJ_shift     0
> pe_solution.tcl:set lj1_shift  [expr
> -4.0*$lj1_epsilon*(pow($lj1_cut,-12)-pow($lj1_cut,-6))]
> pe_solution.tcl:set lj2_shift  [expr
> -4.0*$lj2_epsilon*(pow($lj2_cut,-12)-pow($lj2_cut,-6))]
> 
> So, kremerGrest.tcl is the only correct sample, but we have a 
> whole variety of wrong examples... Does anybody see a problem 
> if I just fix all the scripts?
> 
> Many regards,
> Axel
> 
> --
> Dr. Axel Arnold
> FOM Institute for Atomic and Molecular Physics
> Kruislaan 407                                 Phone: +31 20 6081 275
> 1098 SJ Amsterdam, The Netherlands            E-mail: address@hidden
> 
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