task gradient failed


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Hi...I am new to nwchem ...As I am trying to do task SCF with tweleve Au atoms with one Cr in center...but getting an error in the end of the compilation of the input file i.e



scf_gradient: scf energy failed        0
------------------------------------------------------------------------
This type of error is most commonly associated with calculations not reaching convergence criteria
------------------------------------------------------------------------
For more information see the NWChem manual at http://nwchemgit.github.io/index.php/NWChem_Documentation


As my input file is

title "Au-Cr scf geometry optimization"
charge 0
memory total 800 heap 200 stack 200 global 400 mb
geometry units angstoms print xyz autosym

Au 22.76000 -17.51900 -23.53900
Au 22.79300 -17.55300 -17.96000
Au 24.18900 -19.50800 -19.39000
Au 21.36500 -15.56400 -22.10800
Au 24.32500 -15.57700 -21.97200
Au 21.22800 -19.49500 -19.52600
Au 20.40600 -18.32200 -21.94800
Au 25.14800 -16.75100 -19.55000
Au 25.10600 -18.42900 -21.95700
Au 20.44900 -16.64400 -19.54200
Au 22.75100 -15.05800 -19.53100
Au 22.80300 -20.01500 -21.96700
Cr 22.77700 -17.53600 -20.75000
end
basis
Cr library cc-pvdz
Au library lanl2dz_ecp
end
ecp
Au library lanl2dz_ecp
end
scf
thresh 1.0e-4
level nr 0
maxiter 50
end
task scf optimize

Please help me to solve error.....
Thanks in advance
Regards
Satvinder