| 10:10:25 AM PST - Wed, Dec 5th 2012 |
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OK, based on Edo's response to my confusion, I went back to the maths to see where I may be thinking about this incorrectly.
One peculiarity of NWChem seems to be that the geometry is always aligned along the y-axis via the a2 vector. These test cases illustrate this apparent outcome (all for lat_a = lat_b = lat_c = 1.0):
Lattice Parameters
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a1=< 0.707 0.707 0.000 >
a2=< 0.000 1.000 0.000 >
a3=< 0.000 0.000 1.000 >
a= 1.000 b= 1.000 c= 1.000
alpha= 90.000 beta= 90.000 gamma= 45.000
Lattice Parameters
------------------
a1=< 1.000 0.000 0.000 >
a2=< 0.000 1.000 0.000 >
a3=< 0.707 0.000 0.707 >
a= 1.000 b= 1.000 c= 1.000
alpha= 90.000 beta= 45.000 gamma= 90.000
Lattice Parameters
------------------
a1=< 1.000 0.000 0.000 >
a2=< 0.000 1.000 0.000 >
a3=< 0.000 0.707 0.707 >
a= 1.000 b= 1.000 c= 1.000
alpha= 45.000 beta= 90.000 gamma= 90.000
Lattice Parameters
------------------
a1=< 1.000 0.000 0.000 >
a2=< 0.000 1.000 0.000 >
a3=< 0.707 0.707 0.000 >
a= 1.000 b= 1.000 c= 1.000
alpha= 45.000 beta= 45.000 gamma= 90.000
Lattice Parameters
------------------
a1=< 0.707 0.707 0.000 >
a2=< 0.000 1.000 0.000 >
a3=< -0.707 0.707 0.000 >
a= 1.000 b= 1.000 c= 1.000
alpha= 45.000 beta= 90.000 gamma= 45.000
Lattice Parameters
------------------
a1=< 0.707 0.707 0.000 >
a2=< 0.000 1.000 0.000 >
a3=< 1.000 0.000 0.000 >
a= 1.000 b= 1.000 c= 1.000
alpha= 90.000 beta= 45.000 gamma= 45.000
Lattice Parameters
------------------
a1=< 0.707 0.707 0.000 >
a2=< 0.000 1.000 0.000 >
a3=< 0.293 0.707 0.644 >
a= 1.000 b= 1.000 c= 1.000
alpha= 45.000 beta= 45.000 gamma= 45.000
What was throwing me was that I intuitively expected a1 to remain the base, rather than a2, so when I have a non-right-angle gamma, I expected to see the change in a2, not a1. In my case, this means that I have to figure a1 from a2, instead of the other way around, as a2 will apparently align with the y-axis no matter what in NWChem.
Thanks a lot, Edo.
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