• ## Outreach

From: Aiswarya (aiswarya.pawar_at_gmail.com)
Date: Thu Oct 09 2014 - 13:32:55 CDT

Dear Users,
Am trying to calculate rotational angle for a given 4 atoms, am getting the value of angle correct but its not differentiating between +ve and -ve. Ie if the angle between 4 atoms is -177 degrees am getting 177 degree, and there is no -ve sign to it. Below is the script i have used.

> # Computes the dihedral angle of a bond
>
> set coord1 [lindex [[atomselect top "index 86" ] get {x y z}] 0]
> set coord2 [lindex [[atomselect top "index 89" ] get {x y z}] 0]
> set coord3 [lindex [[atomselect top "index 75" ] get {x y z}] 0]
> set coord4 [lindex [[atomselect top "index 23"] get {x y z}] 0]
> set v1 [vecsub \$coord1 \$coord2]
> set v2 [vecsub \$coord3 \$coord2]
> set v3 [vecsub \$coord4 \$coord3]
>
> set cross1 [vecnorm [veccross \$v2 \$v1]]
> set cross2 [vecnorm [veccross \$v2 \$v3]]
> set cos [vecdot \$cross1 \$cross2]
> set rotvec [veccross \$cross1 \$cross2]
> set sin [veclength \$rotvec]
> set angle [expr atan2(\$sin,\$cos)*(180.0/3.14)]
> return \$angle

Please someone tell me were am going wrong.

Thank you so much,
Aiswarya