  Glycine on Cu(001) is used as an example to illustrate the critical role of
molecular polarity and finite temperature effect in self-assembly of
biomolecules at a metal surface. A unified picture for glycine self-assembly on
Cu(001) is derived based on full polarity compensation considerations,
implemented as a generic rule. Temperature plays a non-trivial role: the
ground-state structure at 0 K is absent at room temperature, where
intermolecular hydrogen bonding overweighs competing molecule-substrate
interactions. The unique p(2X4) structure from the rule is proved as the most
stable one by ab initio molecular dynamics at room temperature, and its STM
images and anisotropic free-electron-like dispersion are in excellent agreement
with experiments. Moreover, the rich self-assembling patterns including the
heterochiral and homochiral phases, and their interrelationships are entirely
governed by the same mechanism.
