Expectation value of S2


Click here for full thread
Clicked A Few Times
Hi all I am running a constrained geometry optimization of a compound I heme with a furan in the doublet spin state. I am running on a linux machine with CentOS7.1, compiled as instructed without ELPA and with all patches applied. However, my output file says

      <S2> =      1.6116 (Exact =     0.7500)


which is much higher than expected. How can there be so much spin contamination!?


My input file:

start
title "name"
geometry
 load furan2ts.xyz
end
memory 1000 mb
basis
 *  library 6-31G*
 Fe library ahlrichs_pvdz
end
dft
 xc b3lyp
 mult 2
 iterations 300
 direct
end
geometry adjust
 zcoord
  bond 43 44 1.9 constant
 end
end
driver
 xyz consgeo
 maxiter 300
end
task dft optimize


and coordinates:

   52
FINAL HEAT OF FORMATION =     0.000000
Fe     0.245686     0.523085    -0.169481
 C    -2.294074     2.305041     1.275323
 H    -3.103504     2.853202     1.747683
 C     2.507512     2.808116     1.049268
 H     3.226456     3.513876     1.453739
 C     2.772998    -1.075288    -1.814767
 H     3.567741    -1.594022    -2.341870
 C    -2.021229    -1.696198    -1.433637
 H    -2.732564    -2.418112    -1.822171
 N     0.128301     2.236264     0.920817
 C    -1.007652     2.797882     1.438037
 C    -0.677599     3.975677     2.206659
 H    -1.400682     4.602190     2.713431
 C     0.673917     4.110223     2.152554
 H     1.296967     4.871711     2.604402
 C     1.168255     3.016879     1.347852
 N     2.243754     0.802537    -0.339881
 C     2.997436     1.777733     0.261343
 C     4.392253     1.604853    -0.071994
 H     5.190967     2.247346     0.276570
 C     4.469517     0.520282    -0.887789
 H     5.344651     0.081221    -1.349867
 C     3.121406     0.027818    -1.048328
 N     0.349211    -1.051054    -1.367373
 C     1.484136    -1.563920    -1.962949
 C     1.146205    -2.710452    -2.764970
 H     1.859472    -3.288190    -3.339277
 C    -0.198794    -2.891110    -2.652904
 H    -0.819370    -3.648772    -3.114660
 C    -0.689433    -1.853759    -1.784218
 N    -1.751168     0.340986    -0.102551
 C    -2.510971    -0.661775    -0.648052
 C    -3.901729    -0.473335    -0.315417
 H    -4.704792    -1.125489    -0.635574
 C    -3.973949     0.658413     0.436540
 H    -4.848674     1.128923     0.867726
 C    -2.628374     1.160858     0.567527
 S     0.042738     2.007223    -2.004140
 C    -1.020853     1.228563    -3.269307
 H    -1.112504     1.952272    -4.086365
 H    -0.581248     0.309571    -3.666945
 H    -2.021766     1.013412    -2.884872
 O     0.483013    -0.248634     1.367937
 C     0.646216    -1.864634     2.143764
 O     0.932691    -2.893248     1.173337
 C    -0.171425    -3.694093     0.996863
 C    -1.201663    -3.284412     1.851715
 C    -0.609907    -2.086991     2.720575
 H    -0.144944    -4.502802     0.274530
 H     1.489652    -1.502744     2.722584
 H    -2.031087    -3.741400     1.846584
 H    -0.940205    -1.492595     3.379670