.. _config_ref tasks md ssrestraints:

``ssrestraints``
================

Secondary-structure restraints generated by the VMD ssrestraints plugin and applied via NAMD's extraBonds facility

Single-valued attributes:

  * ``sel``: VMD atomselect text passed to ssrestraints -sel; restricts which residues are restrained (default: helix or extended_beta or nucleic)

  * ``k_prot``: Force constant for protein phi/psi dihedral restraints (kcal/mol/rad^2) (default: 200)

  * ``k_na_dih``: Force constant for nucleic-acid backbone dihedral restraints (kcal/mol/rad^2) (default: 200)

  * ``k_na_bond``: Force constant for nucleic-acid base-pair bond restraints (kcal/mol/A^2) (default: 200)

  * ``na``: Nucleic-acid restraint mode: 0=all-residue dihedrals; 1=base-paired-residue dihedrals; 2=base-pair bonds; 3=both 1 and 2 (default: 3)

  * ``ideal``: Use ideal phi/psi for alpha/3-10 helix and beta strand instead of measured values (default: False)

  * ``hbonds``: Add backbone H-bond bond+angle restraints (default: False)

  * ``hbdonorsel``: VMD atomselect text identifying H-bond donor heavy atoms (default: name N and backbone and (helix or extended_beta))

  * ``hbaccsel``: VMD atomselect text identifying H-bond acceptor heavy atoms (default: name O and backbone and (helix or extended_beta))

  * ``hbbondk``: Force constant for the H-bond bond term (kcal/mol/A^2) (default: 20.0)

  * ``hbanglek``: Force constant for the H-bond angle term (kcal/mol/rad^2) (default: 20.0)

  * ``hbdcut``: H-bond donor-acceptor distance cutoff used during detection (Å) (default: 3.5)

  * ``hbacut``: H-bond donor-H-acceptor angle cutoff used during detection (degrees) (default: 35.0)



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