Trouble with negative frequencies

memory stack 1750 mb heap 100 mb global 425 mb noverify

geometry 
  Sn                    2.83057294     0.00000000     1.79084262
  Sn                    1.48326322    -2.28741950     0.38664881
  Sn                    2.53215310     0.00000000    -1.48542974
  Sn                    0.00000000     0.00000000     2.49952371
  Sn                    1.48326322     2.28741950     0.38664881
  Cu                    0.00000000     0.00000000    -0.10161326
  Sn                   -2.83057294     0.00000000     1.79084262
  Sn                   -1.48326322    -2.28741950     0.38664881
  Sn                    0.00000000    -1.59009764    -2.29900451
  Sn                    0.00000000     1.59009764    -2.29900451
  Sn                   -1.48326322     2.28741950     0.38664881
  Sn                   -2.53215310     0.00000000    -1.48542974
 zcoord ; cvr_scaling 0.85d0 ;end
end

basis spherical
* library cc-pvtz-pp
end

ecp
* library cc-pvtz-pp
end
set tolguess 1d-3
dft
 mult 2
 xc pbe0
 convergence energy 5d-9 damp 45 ncydp 0 dampon 1d99 dampoff 1d-4
 smear
 grid fine
 maxiter 999
end

driver
 clear
 tight
end

task dft optimize
set int:txs:limxmem               29379684
dft
grid Sn 750 18 Cu 400 18
end
task dft freq