Gaussian09 Secret Code ? Morokuma Energy Decomposition

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As the Gaussian 16 was released earlier this year, the HP of Gaussian was renewed.

All IOp Reference also became g16 compatible, and the IOp manual for g09 has disappeared. . . (The IOp of g16 and g09 is slightly different.)

We think that some people regret that I had to download the IOp manual of g09, but you don’t need to worry about it!

All IOp are written in the Gaussian’s source code! !


See L101.F !

For example, when looking into L101.F, the comments about Link is written first. As you continue reading, the explanation of IOp started from around line 120. By the way, the format is exactly the same as IOp Reference.

In L101.F, IOp information on overlay 1 is written.

In L202.F, IOp information on overlay 2 is written.

Likewise, you can also find other overlay’s IOp.

Morokuma-Kitaura energy decomposition analysis

Reading the description about IOp in the source code, it is interesting that there are many IOp which are not listed in the IOp manual which is distributed in general!

For example, if you look at the point corresponding to IOp 1/160 = 30, there is a statement

30 … Morokuma energy decomposition.

Generally, it is common to use other software such as GAMESS for Morokuma-Kitaura energy decomposition analysis in calculating steric repulsion etc. It is said that it is not available to use it in Gaussian…

However, as you can see the Gaussian source code, there is an evidence that it seemed to be implemented. But even if you actually specify iop (1/160 = 30) and run it, you can’t get anything…

Considering that this IOp 1/160 = 30 is not on the manual for public, it seems that Gaussian tried to implement it at the development stage, but was not eventually implemented? However, the truth is in the dark….

How about in Gaussian16?

Iop 1/160 which was not used in g09, but it is described in the manual for general in g16.

As we mentioned above, in g09, the description on iop = (1/160 = 0, 1, 2, 10, 20, 30, 40, 50, 60, 70) was found in the source code, but it was not written in the general manual . . .

In g16, there was only description about iop = (1/160 = 0, 1, 2, 10, 20, 80, 0xxx, 1xxx, 2xxx), and the Morokuma energy decomposition ( 1/160 = 30 ) was deleted. . .

It is unclear if Gaussian will implement energy decomposition or not, , but it will be useful if you can use it in Gaussian!

If someone knows how to use Morokuma-Kitaura energy decomposition analysis in Gaussian, please let us know by comment or email?

When you get tired of calculation, I recommend you reading the Gaussian source code! It must be interesting and productive! In this article, we introduced the comment section in the source, so even if you are not familiar with programming, you can understand.

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  1. In the Multiwfn’s manual, you could find a way to obtain the EDA combining both programs, Multiwfn and Gaussian:

    In the TOC the important sections explaining the steps to perform are:

    “3.100.8 Generate Gaussian input file with initial guess from fragment wavefunctions”

    “4.100.8 Perform simple energy decomposition by using combined fragment wavefunctions”

    Best regards

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