i have a code 

#!perl

use strict;
use Getopt::Long;
use MaterialsScript qw(:all);

################ Input ####################
my \\\$doc = \\\$Documents{"1010.xtd"}; # xtd file name
#\\\$doc->CurrentFrame = \\\$doc->EndFrame; # frame number of xtd file (end frame)
\\\$doc->CurrentFrame = 1201; # frame number of xtd file (user defined frame number)
\\\$doc->GenerateLatticeDisplay(["PeriodicDisplayType" => "In-Cell"]); # Display mode
###########################################

my \\\$std = Documents->New("1010.std");

\\\$std->ColumnHeading(0) = "Element Symbol";
\\\$std->ColumnHeading(1) = "Position X (angstrom)";
\\\$std->ColumnHeading(2) = "Position Y (angstrom)";
\\\$std->ColumnHeading(3) = "Position Z (angstrom)";
\\\$std->ColumnHeading(4) = "Velocity X (angstrom/ps = 100m/s)";
\\\$std->ColumnHeading(5) = "Velocity Y (angstrom/ps = 100m/s)";
\\\$std->ColumnHeading(6) = "Velocity Z (angstrom/ps = 100m/s)";
\\\$std->ColumnHeading(7) = "Kinetic E of atom (eV)";

my \\\$atoms = \\\$doc->UnitCell->Atoms; #scalar 
my \\\$i = -1;
my \\\$AvoN = 6.02*10**23;
my \\\$KJmolToeV = 96.5;
my @atoms; #

foreach my \\\$atom (@\\\$atoms) {
my \\\$vel = \\\$atom->Velocity;
#my \\\$atomicnumber = \\\$atom->AtomicNumber;

if(\\\$atom->ElementSymbol eq "H"){
\\\$i = \\\$i + 1;
print "Element symbol = ", \\\$atom->ElementSymbol, " Position = ", \\\$atom->X, \\\$atom->Y, \\\$atom->Z, " Velocity =", \\\$vel->x, \\\$vel->y, \\\$vel->z, "\\n";
\\\$std->Cell(\\\$i,0) = \\\$atom->ElementSymbol;
\\\$std->Cell(\\\$i,1) = \\\$atom->X;
\\\$std->Cell(\\\$i,2) = \\\$atom->Y;
\\\$std->Cell(\\\$i,3) = \\\$atom->Z;
\\\$std->Cell(\\\$i,4) = \\\$vel->x;
\\\$std->Cell(\\\$i,5) = \\\$vel->y;
\\\$std->Cell(\\\$i,6) = \\\$vel->z;
\\\$std->Cell(\\\$i,7) = 0.5*((\\\$vel->x)**2+(\\\$vel->y)**2+(\\\$vel->z)**2)*10**-4;
}
 
if(\\\$atom->ElementSymbol eq "H" and 0.5*((\\\$vel->x)**2+(\\\$vel->y)**2+(\\\$vel->z)**2)*10**-4 < 0.0005){
push(@atoms, \\\$atom);
}
 
}
\\\$doc->CreateSet("absorbedH", \\@atoms);

this code works well, but just only got atoms velocitiy,

i want to know "H2" 's Net velocity how can i do for?