How to do properly an optimization with constraints?

[ouielba90]

I have a molecule that is in an SDF format and I want to optimize it using constraints. I have added the following lines in the SDF fine and then I simply run xtb molecule.sdf --opt,

$constraint
dihedral: 23, 24, 25, 7, 0
$end

But the program ignores it. I also tried to put these lines in an input file (input.inp) and then run xtb molecule.sdf --input input.inp, yet I got the same issue.

What am I doing wrong?

[TyBalduf]

I'm not sure of your first command, do you mean you put $constrain ... on the commandline?

If so, I believe you just need to do xtb molecule.sdf --opt --input input.inp. The xcontrol input sets input parameters, but doesn't turn on particular calculation types, i.e you still need to specify opt to get it to start an optimization and then the setting a constraint will constrain that bond/angle/dihedral during the opt.