CHIV V [0] s [0.2] atomnamesThe chiral volumes of the named atoms are restrained to the value V (in cubic Angstroms) with standard deviation s. The chiral volume is defined as the volume of the tetrahedron formed by the three bonds to each named atom, which must be bonded to three and only three non-hydrogen atoms in the connectivity list; the order in the connectivity list, which is determined by the order of increasing bond lengths, defines the sign of the chiral volume. Note that RTAB may be used to list chiral volumes defined in the same way but without restraining them. The chiral volume is positive for the alpha-carbon (CA) of an L-amino-acid if the order of the three bond lengths is CA-N, CA-C, CA-CB (as would be expected for an accurate structure). Note that 'CHIV 0' (or just CHIV since the default V is zero) may be used to impose a planarity restraint on an atom which is bonded to three others (by making the chiral volume zero), and is mathematically equivalent to a FLAT instruction which names the four atoms explicitly.
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