Dear all,

When I geometry optimize my crystal structure in P1 symmetry, I obtain the following lattice parameters:

a = 4.049465 Å

b = 4.048257 Å

c = 6.743723 Å

α = 83.923486°

β = 83.865180°

γ = 62.441285°

Cell volume = 97.247146 ų

However, when I allow CASTEP to convert the structure to a higher-symmetry setting (using the prompt at the beginning of the geometry optimization), I get:

a = 4.049562 Å

b = 4.049562 Å

c = 9.046694 Å

α = 125.162434°

β = 125.162434°

γ = 62.433003°

Cell volume = 97.225825 ų

My question is: Why are the lattice parameters different? Shouldn't the final geometry be the same regardless of whether symmetry is imposed or not? I’ve always thought that imposing symmetry merely reduces computational time without affecting the physical outcome.

While the cell volumes are almost identical, there are noticeable differences in the c lattice parameter and the lattice angles.

I'm using Materials Studio 2024, and I observe this behavior regardless of the functional, geometry optimization settings, or tolerances used.

Any insights would be greatly appreciated.

Best regards,