Phase diagrams as a function of anisotropy D and magnetic field H are obtai
ned for discommensurations and surface states for an antiferromagnet in whi
ch H is parallel to the easy axis, by modeling it using the ground states o
f a one-dimensional chain of classical XY spins. A surface spin-flop phase
exists for all D, but the interval in H over which it is stable becomes ext
remely small as D goes to zero. First-order transitions, separating differe
nt surface states and ending in critical points, exist inside the surface s
pin-flop region. They accumulate at a field H' (depending on D) significant
ly less than the value HSF for a bulk spin-hop transition. For H' < H < H-S
F, there is no surface spin-flop phase in the strict sense; instead, the su
rface restructures by, in effect, producing a discommensuration infinitely
far away in the bulk. The results are used to explain in detail the phase t
ransitions occurring in systems consisting of a finite, even number of laye
rs. [S0163-1829(99)02309-7].