Hi,

a colleague of mine did a calculation of CO

_{2} and "for fun" started with a bend structure and just C1 symmetry. As expected the structure became linear after optimization but was of course not aligned on one of the coordinate axes. After this he did an aoforce run and got 4 modes with nonzero frequencies (3*3-5 =4, for me this is a clear sign that Turbomole also accepted the structure as linear). So far so good but the 4 modes had each totally different frequencies but one would expect the two bending modes to be degenerate. The expected result can be obtained by using NumForce (-central) or aligning the molecule along one axis

This behavior was also observed when using all the TM defaults (C1 symmetry, def-SV(P) basis set, HF, coord file

`$coord`

0.00001227374264 -0.00000003075555 0.00000000000000 c

-2.14857205963009 0.00000001537753 0.00000000000000 o

2.14855978588746 0.00000001537802 0.00000000000000 o

$user-defined bonds

$end

) where I got the following non-zero modes

Method | Freq/cm^{-1} |

aoforce | 757.98 | **1054.69** | 1539.82 | 2630.16 |

grad, NumForce | 754.61 | 763.47 | 1541.23 | 2631.03 |

grad, NumForce -central | 760.82 | 760.82 | 1540.30 | 2631.78 |

aoforce with molecule aligned on x axis | 758.04 | 758.04 | 1539.73 | 2629.94 |

Can you reproduce the results and maybe also give an explanation?

We are still using TM Version 6.3.1 (SMP parallel)