Geometry optimization along one particular axis


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Is there a way to geometry optimize a particular atom/atoms only along one particular axis? For example, in the following input file, I would like to relax O atom only along the z-axis. Thanks.

echo
title cluster 
start cluster
geometry autosym noautoz
Pt -1.39896888 0.86172975 -1.61108607
Pt -0.00922755 -1.57700835 -1.65135907
Pt 1.40819888 0.84574833 -1.61134885
Pt -2.80716904 0.02162492 0.66743369
Pt -1.41742659 -2.41711322 0.62716018
Pt -1.38974210 2.44438247 0.70744393
Pt -0.00000016 0.00564344 0.66717091
Pt 1.38974179 -2.43309557 0.62689689
Pt 1.41742629 2.42840012 0.70718062
Pt 2.80716874 -0.01033804 0.66690712
O -0.00922755 -1.57700835 1.91510617
end

basis "large" cartesian
Pt library lanl2dz_ecp file /usr/local/NWChem/data/libraries/
O library 6-311G** file /usr/local/NWChem/data/libraries/
end

ecp
Pt library lanl2dz_ecp file /usr/local/NWChem/data/libraries/
end
set geometry:actlist 11
set "ao basis" "large"

dft
iterations 1000
direct
XC xpbe96 cpbe96
smear 0.001
end

DRIVER
XYZ a.xyz
MAXITER 500
END
task dft optimize