The potential curve for the helium dimer is very flat and our default geometry optimizer is not very smart under these circumstances.
Please try the input below
echo
start nw
charge 0
geometry
He -8.67636000 -0.30490000 0.00000000 # 1
He -5.71316000 -0.37225000 0.00000000 # 2
end
basis spherical
* library cc-pvtz
end
scf
maxiter 1000
end
dft
xc pbe0
disp vdw 3
grid fine
convergence energy 1d-8
end
driver
clear
TIGHT
eprec 1e-08
maxiter 2000
lbfgs
end
task DFT optimize
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