I want to define a circle around a special atom of a group and then I want to know the number of different atoms inside of this circle at different times .
Can you please let me know how i can do that ?
You can easily do this by post-processing in vmd. Here, the selection is all the H atoms. The code calculates the number of atoms within 3 Å of all the H atoms. You should choose your desired selection and distance.
set mol [molinfo top]
set fp [open “No-atoms.tmp” w]
set n [molinfo $mol get numframes]
for {set i 0} {$i < $n} {incr i} {
puts “\t \t progress: $i/$n”
set a [atomselect top “within 3 of type H” frame $i]
set num [$a num]