### Author Topic: Unit of displacements in TURBOMOLE  (Read 7703 times)

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##### Unit of displacements in TURBOMOLE
« on: November 03, 2009, 10:26:57 AM »
Hi!

I'm wondering what the units of the cartesian displacements in an aoforce calcuation are? a_0, Angstrom oder something completely different?

#### uwe

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##### Re: Unit of displacements in TURBOMOLE
« Reply #1 on: November 03, 2009, 11:55:41 AM »
Hello,

aoforce does the 2nd derivatives analytically, what cartesian displacements do you refer to?

Uwe

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##### Re: Unit of displacements in TURBOMOLE
« Reply #2 on: November 03, 2009, 12:56:40 PM »
The output displacements (normal modes) !

#### uwe

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##### Re: Unit of displacements in TURBOMOLE
« Reply #3 on: November 03, 2009, 02:33:29 PM »
Hi,

the \$vibrational normal modes are the eigenvectors of the Hessian matrix that give the direction of the modes. The vectors are for displacement in the limit -> 0 so to say.

To get coordinates that are moved along a mode, use the script screwer.

Regards,

Uwe

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##### Re: Unit of displacements in TURBOMOLE
« Reply #4 on: November 03, 2009, 03:15:39 PM »
Thank you! That helps!

What are the cartesian gradients printed out by screwer?

#### uwe

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##### Re: Unit of displacements in TURBOMOLE
« Reply #5 on: November 03, 2009, 03:42:44 PM »
Hi,

those from the gradient file - current coordinates, newest gradients from the last gradient calculation or geometry optimization, and the vibrational normal modes are read in to generate the new shifted coordinates.

Uwe

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##### Re: Unit of displacements in TURBOMOLE
« Reply #6 on: November 09, 2009, 10:57:20 AM »
What exactly is this program vibrations doing?

#### uwe

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##### Re: Unit of displacements in TURBOMOLE
« Reply #7 on: November 09, 2009, 05:47:59 PM »
Hi,

it reads in the vibrational normal modes and moves the coordinates along the mode that one can choose. The new coordinates can then for example be used to start a new optimization - useful if you want to get rid of an imaginary frequency.

Regards,

Uwe