Question

In Gaussian 09/16, when rigid scanning two bond distances simultaneously, what input modifications are required for scanning 2 H atoms simultaneously in a water molecule?

Answer 1

In Gaussian 09/16, a rigid scan of two H atoms in H₂O requires modifying the input file to include the ModRedundant keyword and Scan keyword, and defining two B commands for the O-H bond distances to be scanned.

Step-by-step explanation:

In Gaussian 09/16, when performing a rigid scan of two hydrogen atoms in a water molecule, modification to the input file is necessary to define the scan parameters.

Typically, one would use the ModRedundant keyword to specify which bonds and angles are to be scanned and at which intervals. For a water molecule (H₂O), you will need to define two B commands in the input file to indicate the two O-H bond distances that you want to scan simultaneously.

If you wish to scan both hydrogen atoms over the same range and at the same intervals, you can specify the same parameters for both B commands. Besides this, you should also specify the Scan keyword, which tells Gaussian to perform a potential energy surface scan over the specified coordinates.