Using Molden with GAUSSIAN

When using Molden with GAUSSIAN 94/98 the following keywords are required on the GAUSSIAN 94/98 inputfile:
```
    #P GFINPUT IOP(6/7=3)
```
#P switches on printing of SCF convergence, GFINPUT switches on printing of Basis Set info, and IOP(6/7=3) switches on printing of all MO's. GAUSSIAN 94/98 per default uses the redundant coordinates optimization procedure resulting in only cartesian coordinates being available on the output file. Molden will covert these into a z-matrix which in general will have lost the dummys and therefore symmetry at the z-matrix level. Use the gaussian keyword opt=z-matrix to get z-matrices on the output.
When using Molden with GAUSSIAN 92 and older versions, use:
```
    #P GFINPUT IOP(6/7=1)
```
Never use output of compound jobs (f.i. an optimisation followed by a frequency calculation, gaussian keywords opt freq ). You should split up the output of compound jobs into separate files, for Molden to work correctly.
Molden will warn you:
```
 WARNING: composite optimisation/frequency job
 The frequency job should be a separate file
 With First line:
  
  Entering Gaussian System
```
To split up the file, look for the string Normal termination of Gaussian , this is the end of the first run, now split the file up in two parts. (In the vi editor:
```
/Normal termination
:.,$w output2
:.,$d
:x
```
)
Be sure to add the following line to the second file:
```
 Entering Gaussian System
```
If you use the non-split up output, the geometrie optimisation structures will not be updated when youe use the next or movie buttons.
Some parts of Molden do not support the use of 5D functions (The Electrostatic potential, esp charges, Distributed Multipole Analysis and Mulliken Charges), therefore it is recommendable to use the 6D Gaussian keyword in conjuction with Molden.
Molden does not support the use of Effective Core Potentials. Although the orbitals of such a calculation can be visualised and are valid.
Beware of using non-readible characters on the output (such as the date in russian), molden will think it is dealing with a binary format (mopac .gpt or msf).
The use of #T (Terse output) can give problems with molden.
For Gaussian98 and upwards the default is to print the Z-matrix and resultant coordinates ONLY for 50 atoms or less. To have Gaussian98 also print this information if the number of atoms is bigger than 50, add the following keywords:
```
    IOP(2/11=1)
```
When gaussian reads the basisset from cards (/gen option) be sure to have the correct contraction coefficients. Gaussian will renormalize after it has printed the basisset, causing molden to use the wrong contraction coefficients.
When doing MP2 calculations and you want molden to read the MP2 density add the gaussian keyword: pop=(naturalorbitals)
There is an awk script ircextract.awk that will let you extract only the optimised structures from an gaussian98 run, to run it type:
```
awk -f ircextract.awk output.g98 > output.irc
```
The file output.irc is a concatenation of xyz files, which you can read back into molden and view it with molden via the movie and next buttons.
With courtesy of Dr. Rafael R. Pappalardo, Dept. Quimica Fisica, Fac. de Quimica, Univ. de Sevilla.
Molden (3.5 and upwards) supports Gaussian Cube files. Start molden without a file specified on the commandline. Go to the density mode, and click "cube file". You should not specify the cube file on the commandline. The default molden version can handle grids of maximum dimension 61x61x61. Often gaussian cubes are bigger, you will have to create a new version of molden to handle these. In the tarred source distribution there is a csh script 'change_parameter' edit it and make the central part look like:
```
cat < /tmp/sed.tmp
1,\$s/mx3d=61/mx3d=122/
EOF
```
Now execute the script, type ./change_parameter, and recompile by typeing make, you will have an executable dimensioned for a maximum grid size 122x122x122.
NOTE: not all values will work due to the way it is programmed in fortran, if f.i. 130 doesnt work try 131 or 132
You should use the molden keyword GAUCUB=filename instead of the molden keyword FILE=filename to specify a cube file in the keyword mode.
Molden3.6 uses dynamic memory allocation for the grid, so that you should no longer encounter this situation