hcp lattice problem

Dear all;

I have noticed that hcp defined in lammps manual is different from hcp lattice that we define in crystallography (for example the former has 4 basis atoms when the later one has 6 basis atoms). My question is about simulating Ti that has a hcp structure. Can i use "lattice hcp " command for my purpose or should I use “lattice custom”? If it is possible to use the “lattice hcp” command, what should be the scale? for metal units, scale is lattice constant in distance units and it is for cubic structures. but for example for Ti with an orthogonal structure we have a=b=2.95 and c=4.686 (A).
I have gone through mail list concerning this matter and there were some cases in which it was suggested to use “lattice custom” command. But even this cannot simulate hcp lattice with 6 basis atom since we need 4 primitive vector to define such a structure.
after all, since I wanna use the EAM potential file presented for Ti (with a hexagonal structure), I guess it would be necessary to define the lattice as a hcp with 6 basis atom.

Thank you for your help.

The hcp defined by LAMMPS has a specified c/a ratio, as explained
on the doc page. If you want something different use the custom
option. You can define any unit cell you wish, with as many basis
atoms as you wish, via custom. All the lattice command is
used for in this context is to create atoms at locations. It
has no "crystallographic meaning" that LAMMPS uses for
anything else. If your structure is a periodic lattice, then
the lattice command should be able to create it.