RE: [ESPResSo] Radius of Gyration

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

You have to use the analyze set chains command before using analyze rg.
See ug chapter Analysis->Topologies->Chains
Hanjo 

> -----Original Message-----
> From: address@hidden 
> [mailto:address@hidden On Behalf Of 
> Lorenzo Isella
> Sent: vendredi, 7. décembre 2007 17:03
> To: address@hidden
> Subject: [ESPResSo] Radius of Gyration
> 
> Dear All,
> I have a problem when dealing with a test case (small system 
> with a few particles). For some reason, the calculation of 
> the radius of gyration returns NaN at any time. This has 
> nothing to do with my previous mail (I have not installed any 
> CVS version of Espresso).
> Consider for instance the following code:
> 
> set n_part 10; #set density 0.00002
> #set box_l [expr pow($n_part/$density,1./3.)]
> 
> set box_l 20.
> set volume [expr pow($box_l,3.)]
> 
> set density [expr $n_part/$volume ]
> 
> puts "the density is, $density"
> 
> 
> set magnification 1.
> 
> setmd box_l [expr $magnification*$box_l] [expr 
> $magnification*$box_l] [expr $magnification*$box_l] setmd 
> periodic 1 1 1
> 
> puts "the box side is, $box_l"
> 
> 
> set q 0; set type 0
> 
> # I now set the particle charge to 0 and see if the code 
> works the same of not
> 
> for {set i 0} { $i < $n_part } {incr i} { set posx [expr 
> $box_l*[t_random]] set posy [expr $box_l*[t_random]] set posz 
> [expr $box_l*[t_random]]
> 
> part $i pos $posx $posy $posz q $q type $type }
> 
> puts "Ok after allocating a few particles"
> 
> set tot_time 1000.
> 
> 
> set my_step 0.01
> 
> 
> set N_step [expr $tot_time/$my_step]
> 
> set N_step [expr round($N_step)]
> 
> 
> set integ_steps 1
> 
> # number of configurations I want to save
> 
> set N_save 1000
> 
> #I save a configuration every time steps
> 
> set every [expr $N_step/$N_save]
> 
> puts "every is, $every"
> 
> 
> 
> puts "the total number of time steps is, $N_step"
> 
> 
> setmd time_step $my_step; setmd skin 0.4 set temp 2. ; set gamma  1.
> thermostat langevin $temp $gamma
> 
> set sig 1.0
> set cut 1.1
> set eps 20.
> set shift 0.
> #set e1 12.
> #set e2 10.
> set r_off 0.
> set omega 0.3
> 
> #inter 0 0 lj-cos2 $eps $sig $cut $shift $r_off $e1 $e2
> 
> inter 0 0 lj-cos2 $eps $sig $r_off $omega set tau_increase 10.
> 
> set delta_t [expr $integ_steps*$my_step]
> 
> puts "delta_t is, $delta_t"
> 
> set cap_ini 20.
> set cap_fin 200.
> set delta_cap [expr $cap_fin-$cap_ini]
> set lin_coeff [expr $delta_cap/$tau_increase]
> 
> set n_iter_cap [expr $tau_increase/$delta_t]
> 
> set n_iter_cap [expr round($n_iter_cap)]
> 
> puts "the number of iterations while ramping the potential 
> is, $n_iter_cap"
> 
> 
> puts "delta_cap is, $delta_cap"
> 
> set cap $cap_ini
> 
> for {set i 0} { $i <= $n_iter_cap } { incr i} { puts 
> "t=[setmd time] E=[analyze energy total]"
> inter ljforcecap $cap; integrate $integ_steps
> 
> set cap  [expr $cap + $lin_coeff*$delta_t ]
> 
> set min [analyze mindist]
> 
> }
> 
> puts "Warmup finished. Minimal distance now $min"
> 
> set rg_temp [analyze  rg ]
> puts "the radius of gyration is, $rg_temp"
> 
> I am just allocating a few particles in a small box letting 
> them interact via a Lennard-Jones potential.
> Why is the calculation of the radius of gyration failing?
> Kind Regards
> 
> Lorenzo
> 
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