My Community

So, this is probably a rather basic question but after searching Google for a good hour, I still haven't quite been able to figure it out. I was going over the VASP workshop slides and came across the POSCAR file for the Ni- FCC (111) structure.

Ni - (111)
3.53
.70710678 .0000000 .000000
-0.35355339 0.6123724 .000000
.000000 .000000 5.196152
5
selective dynamics
direct
.00000000 .00000000 .00000000 F F F
.33333333 .66666667 .11111111 F F F
.66666667 .33333333 .22222222 F F F
.00000000 .00000000 .33333333 T T T
.33333333 .66666667 .44444444 T T T

I'm not able to figure out where the values for the lattice vectors and the fractional coordinates come from. How exactly are they calculated/determined and how does one know which layers to relax? Any help or a nudge in the right direction would be greatly appreciated.

So, here's an attempt to narrow down the question. I understand where the x and y positions for the fractional coordinates come from and I understand why they are repeating (ABC structure). What I'm not sure is how the z position is determined and which layers are relaxed.

In addition, I understand bits and pieces of the lattice vectors but am not sure about certain values (like the negative sign in -0.354 and the 5.196 in the last vector).

If someone could explain the above, that would be great. Thanks!

Having look at numbers is not very useful. Multiply the cell in x and y dimension and display the structure using some graphical software. This will give answer to your questions.