VMD-L Mailing List

From: Sebastian Stolzenberg (s.stolzenberg_at_fu-berlin.de)
Date: Mon Sep 22 2014 - 10:22:13 CDT

Dear All,

1.)
In the Solvate Plugin, I came across the
::Solvate::rotate_save_water
procedure, which rotates a given system along the z and x axes to find
the orientation with minimum surrounding cuboid volume V0.
I was wondering why this rotation is not performed along all three
cartesian axes to allow the algorithm to find even smaller values of V0.

As an example, I am attaching (below as text) a tcl script I wrote to execute this task
for the "2D8R" PDB structure:
As a result, I obtain a 15% reduced volume compared to the one obtained
from ::Solvate::rotate_save_water.
When I further solvate this system with a 20A water buffer layer (not
shown), the total number of atoms is reduced by 29% compared to the
solvated system produced by the solvate plugin.

2.)
At http://www.ks.uiuc.edu/Research/vmd/plugins/solvate/
I read:
"Because the solvation box must be oriented along the cardinal axes,
this can result in significant system size reductions, but should not be
used if the initial orientation was chosen to facilitate analysis"
I don't quite understand the last half sentence, what kind of situations
does it specifically refer to?

Thank you very much, Best,
Sebastian

#################################################

set mypdb 2D8R
set logstr ""

proc getboxV {mysel} {
        set tmp [measure minmax $mysel]
        set L_x [expr [lindex [lindex $tmp 1] 0] - [lindex [lindex $tmp 0] 0]]
        set L_y [expr [lindex [lindex $tmp 1] 1] - [lindex [lindex $tmp 0] 1]]
        set L_z [expr [lindex [lindex $tmp 1] 2] - [lindex [lindex $tmp 0] 2]]
        return [expr $L_x*$L_y*$L_z]
}

mol load webpdb $mypdb
set allsel [atomselect top "not water"]
set logstr "${logstr}box volume (initial): [getboxV $allsel]\n\n"
$allsel writepdb $mypdb.pdb
$allsel delete

package require solvate 1.5
set mylog [open "solvate_rotate.log" w]
array set bounds { -x 0 +x 0 -y 0 +y 0 -z 0 +z 0 }
::Solvate::rotate_save_water $mypdb.pdb "not water" 36 $mylog
close $mylog
set allsel [atomselect top all]
set logstr "${logstr}box volume (solvate,rotate_z_x): [getboxV $allsel]\n\n"
set V0zx [getboxV $allsel]
$allsel delete

mol delete all
mol load pdb $mypdb.pdb
set allsel [atomselect top all]
$allsel moveby [vecsub {0.0 0.0 0.0} [measure center $allsel]]
set logstr "${logstr}box volume (initial): [getboxV $allsel]\n\n"

set N_rot 36
set d_phi [expr 360.0/$N_rot]
set d_theta [expr 360.0/$N_rot]
set d_gamma [expr 360.0/$N_rot]
set V0 [getboxV $allsel]
set bufcoord [$allsel get {x y z}]
set kV1 0
set kV2 0
set kV3 0
for {set k1 1} {$k1 < [expr $N_rot + 1]} {incr k1} {
   $allsel move [trans axis z $d_phi deg]
   for {set k2 1} {$k2 < [expr $N_rot + 1]} {incr k2} {
     $allsel move [trans axis x $d_theta deg]
     for {set k3 1} {$k3 < [expr $N_rot + 1]} {incr k3} {
       $allsel move [trans axis y $d_gamma deg]
       set V [getboxV $allsel]
       if {$V < $V0} {
         set V0 $V
         set kV1 $k1
         set kV2 $k2
         set kV3 $k3
         set bufcoord [$allsel get {x y z}]
       }
     }
   }
}
puts $V0
$allsel set {x y z} $bufcoord
$allsel writepdb $mypdb.rotate_zxy.pdb
set logstr "${logstr}box volume (rotate_z_x_y): [getboxV $allsel]\n\n"
set V0zxy [getboxV $allsel]

puts $logstr
puts "The system was rotated by [expr $kV1*$d_phi] degrees around Z axis and [expr $kV2*$d_theta] degrees around X axis and [expr $kV3*$d_gamma] degrees around Y axis."
puts "[expr ($V0zx-$V0zxy)/$V0zx]"