When I run geometry optimization of H2O using STO-3G or 3-21G basis set and UHF, the energy components of optimized structure deviate slightly from virial theorem stipulated:
Kinetic energy = 75.424942151953331
Total energy = -75.585962823645531
What could cause this small difference, given that the gradients are pretty close to zero?
Here is the input file used:
molecule h2o {
O
H 1 0.96
H 1 0.96 2 104.5
}
set basis 3-21g
set scf_type pk
set g_convergence GAU_VERYTIGHT
set reference uhf
E, wfn = optimize(‘scf’,return_wfn=True)