  Using first principles methods we calculated the entire {\gamma}-surface of
the first order pyramidal planes in {\alpha}-titanium. Slip on these planes
involving dislocations with c + a dislocations is one means by which
{\alpha}-titanium polycrystals may supplement slip on prism planes with a-type
Burgers vectors to maintain ductility. We find two stable intrinsic stacking
faults with relatively small energies. We show that dissociation of c + a
dislocations into two dislocations with Burgers vectors (c + a)/2 is not
possible in {\alpha}-titanium because there is no stable stacking fault at (c +
a)/2. Instead we propose a possible dissociation of a c + a dislocation into
three partial dislocations separated by the two intrinsic faults we have
identified.
