Anisotropic displacement parameters for H atoms using an ONIOM approach
Charge-density analyses of molecular crystals require an accurate description of the motion of all nuclei, including hydrogens, yet nearly 80% of recent studies treat motion of hydrogen atoms isotropically. Using widely available software we combine
ab initio/molecular mechanics ONIOM cluster calculations with rigid body fits to X-ray ADPs for heavy atoms, to derive ADPs for hydrogens for a variety of molecular crystals. The agreement with neutron diffraction results is impressive, and the method offers considerable promise in future charge-density studies of molecular crystals.
A.E. Whitten and M.A. Spackman
![[ORTEP]](https://www.iucr.org/__data/assets/image/0004/4954/lb5003.gif)
ORTEP comparison between TLS+ONIOM and neutron ADPs for 1-methyluracil at 21 K (99% surfaces). Numbers are values of a similarity index that measures overlap between reference and model probability density functions.
