## sheet() — make a β -sheet

`sheet(atom1, atom2, sheet_h_bonds)`

> This calculates H-bonding restraints for a pair of β -strands. atom1 and atom2 specify the first H-bond in the β -sheet ladder. sheet_h_bonds specifies the number of H-bonds to be added — positive for a parallel sheet, and negative for an anti-parallel sheet. In a parallel sheet, hydrogen bonds start at the first or the second term of the following series (depending on atom1 and atom2): 1N:1O, 1O:3N, 3N:3O, 3O:5N, etc. For an anti-parallel sheet, the corresponding series is 1N:3O, 1O:3N, 3N:1O, 3O:1N, etc. (note that the residue indices run in decreasing order for the second strand in this case). The extended structure of the individual strands themselves is not enforced; use separate strand() restraints if so desired.

> All of the restraints have the `physical.h_bond` physical restraint type, so can be strengthened or weakened by creating a physical.values() object (see also Section 2.2.2).

> To actually add the restraints, pass the new object to Restraints.add(). See Section 2.2.11 for an example.