Need help: MOLUNIT in NBO6

Need help: MOLUNIT in NBO6

Postby Manussada5 » Thu Feb 14, 2019 7:00 am

How to solve the NBO6 define Molecular unit =3 (automatically by NBO6 program) but I need Molecular unit =1

What is the keyword can define Molecular unit =1 and I ever used $nbo MOLUNIT <x,x> $end it doesn't work.

Please help me. Thank you in advanced.

Nus
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Re: Need help: MOLUNIT in NBO6

Postby ericg » Fri Apr 19, 2019 2:41 pm

The MOLUNIT keyword of NBO6 (and 7) allows the user to propose sets of atoms that comprise molecular units. The NBO search will generate no bonds between atoms of one MOLUNIT-defined molecular unit with those of another. However, MOLUNIT cannot ensure that every proposed set of atoms will be described as a single molecular unit of mutually bonded atoms.

For example, suppose you seek to treat the water dimer, (H2O)2, as a single molecular unit, ("MOLUNIT <1-6>", all six atoms in one unit). NBO will calculate two molecular units, despite your MOLUNIT input, because there isn't sufficient bonding character in the electron density to generate a bond between the water molecules.

It may be possible to use the $CHOOSE keylist, instead of MOLUNIT, to specify the bond pattern that you seek for your system, describing it as a single molecular unit. But realize that the NBO search will reject bond patterns that don't reflect the bonding character of the density.

Eric
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