25
votes
What is a good replacement for Gaussian?
ORCA
Official website: https://orcaforum.kofo.mpg.de/app.php/portal
What is ORCA?
ORCA is a general-purpose quantum chemistry program package that features virtually all modern electronic structure ...
- 14.8k
24
votes
What is a good replacement for Gaussian?
OpenMOLCAS
MOLCAS is now in it's 5th decade! The first version was written in the 1980s by the group of Bjorn Roos, one of history's giants in quantum chemistry. It can do many of the things most ...
- 33.1k
18
votes
Retrieving Translational and Rotational Modes
I've never done this myself, and there may be other approaches, but one possible detailed answer seems to be provided by the Gaussian webpage. For stability reasons, you can find this page via the ...
- 1,431
17
votes
Accepted
What are the parameters that need to be calculated to design the structure of a molecule?
Ah, yes, the fun of force-field building.
For the answer to a simple geometry optimization, see I. Camps response below.
Skip to the end if you want what is a more general answer to building an entire ...
- 4,306
17
votes
What is a good replacement for Gaussian?
Psi4
Psi4 is a fully open-source quantum chemistry package that is gaining a lot of interest in my community (computational) combustion chemistry.
Here is the manual for the latest release: it has ...
- 279
16
votes
What is a good replacement for Gaussian?
GAMESS
For many researchers, GAMESS is the "natural" substitute for GAUSSIAN. Developed and maintained by the group of prof. Gordon (also a banned GAUSSIAN user, see image below).
Official ...
- 21.9k
14
votes
Accepted
How can I specify different theory levels for different atoms in Gaussian?
While ONIOM QM/QM is possible, I don't think that is what you want to be doing. From your example input, it looks like you are just trying to use a different basis function on specific atoms, but the ...
- 15k
13
votes
Do bonds between the atoms influence ab-initio energies?
The bonds you draw or see in Gaussview should have no effect on the calculation (besides some minor effects in choosing internal coordinates for a geometry optimization). As you note, a bond is a ...
- 15k
12
votes
How to calculate the band structure of a protein molecule
Band structure is a concept for periodic system only. As proteins are not periodic structures, they don't have electronic bands.
The fact that you can download a PDB file (or a CIF file) with ...
- 21.9k
11
votes
Accepted
Is it possible to do TD-DFT/6-31G+(d,p) calculations on a laptop?
Basis set name versus number of total orbitals
I would like to first address a part of the question that appears to be a misconception about the use of a 6-31+G(d,p) basis set, since you wrote:
"...
- 33.1k
11
votes
What is the meaning of periodic boundary condition for molecular systems?
A periodic boundary condition creates a box around your molecule (or surface) and then treats the molecule leaving the box on the right side as entering the box from the left. This is particularly ...
- 852
11
votes
CCSD(T) Transition State and Ground State Calculations in Gaussian09: "Unable to Determine Lambda"?
It's not a descriptive error message, but this occurs when you reach the max number of iterations for the Eigenvector Following (EF) algorithm and still haven't converged a lambda. While Gaussian uses ...
- 15k
11
votes
What units are used in Gaussian 16 for dipole derivatives output?
I recently had the same question. After emailing Gaussian support I was informed that the units are indeed $\sqrt{\text{km}/\text{mol}}$. From their reply I also believe that the derivatives are ...
- 161
11
votes
Quantum chemistry in external electrostatic field?
Electrostaic embedding is usually on the QM-side as simple point charges which add to the total hamiltonian of the nuceli+electrons. It should be just a simple coulumb interaction.
Any modern ...
- 111
10
votes
What are the parameters that need to be calculated to design the structure of a molecule?
All Gaussian jobs when completed without any error, will have, at the end of the output file, a phrase/thought/quote from someone famous. It is kind off an easteregg. My latest Gaussian successful job ...
- 21.9k
10
votes
Accepted
How to map the electrostatic potential from GAUSSIAN, on a solvent accessible surface?
The Jmol software is able to plot different surfaces.
In the example below, the system is a Mobius strip and the ESP was calculated using MOPAC but as Jmol is full compatible with Gaussian outputs, I ...
- 21.9k
10
votes
How to perform charge analysis for a molecule
This is a very general answer, but let me point you in the right direction at least. If you are looking at a molecular system such as C6H6, you will likely want to use a non-periodic code such as ...
- 10.7k
10
votes
Accepted
What is the precise location of the grid points/voxels in a Gaussian .cube file?
The canonical source is probably Gaussian's user documentation according to which the cube file defines an initial point $(x_0, y_0, z_0)$, as well as three step directions $(x_i, y_i, z_i)$ and the ...
- 17.6k
10
votes
Accepted
What does "Test job not archived" mean?
You are probably running a combined optimisation and frequency job in Gaussian. (I discourage that, but that's a different issue.)
The line means that the calculation preceding it has been run as a ...
- 1,561
10
votes
Accepted
Why does Gaussian ignore the opt=maxcycles keyword for optimizations?
This requires an additional IOP to do. It seems that Gaussian sets a separate lower and upper bound on the number of optimization steps that will be performed based on the number of coordinates and <...
- 15k
10
votes
Accepted
How can I find the parameters in a basis set?
Go to Basis Set Exchange and click on the elements in which you're interested, then click the basis set in which you're interested (in your question, you mentioned 6-31G) and then for "Format&...
- 33.1k
9
votes
How to fix Error Link9999 in Gaussian
TL;DR: There really isn't a straightforward way to fix this error, or a way to guarantee success. This usually involves a very detailed hands-on troubleshooting session, because everything is ...
- 1,561
9
votes
Accepted
Calculate Redox Potential
There are several protocols. Since you mention that you're mostly looking for trends, I'll give the faster method, e.g. by Jason Gilmore:
"Expanding and Testing a Computational Method for ...
- 8,655
9
votes
Accepted
How do I interpret the Gaussian16 wavefunction file?
I have yet to find a source that lays this out explicitly, but from the examples I could find, it is not too hard to infer the meaning of these sections.
To start with (and possibly point you in the ...
- 15k
9
votes
What is a good replacement for Gaussian?
NWChem
Official website: https://nwchemgit.github.io/ and https://www.nwchem-sw.org/
It is open source
Description:
NWChem aims to provide its users with computational chemistry tools that are ...
- 6,436
9
votes
Accepted
Problem obtaining a Raman spectra of a graphene structure
Since you include the command cphf=RdFreq, Gaussian expects you to have entered a perturbation frequency after the rest of the input. You need to specify a ...
- 15k
9
votes
Geometry optimization with Moller-Plesset MP4
Gaussian can do all the way up to MP5 for single-point energies, but analytic gradients are only available for MP2, MP3, MP4(DQ) and MP4(SDQ), the latter including only single, double and quadruple ...
- 33.1k
9
votes
Accepted
Symmetry group of p-benzoquinone
tldr: For a UV/Vis spectra, it shouldn't matter much.
I've found that Gaussian's AM1 / PM3 implementation often breaks symmetry during optimization. So I'm not surprised at your finding.
Moreover, in ...
- 8,655
9
votes
Accepted
Find with grep in terminal last hit in log file
I think this requires piping, see these ServerFault or StackOverFlow questions. For a single file, the two main approaches would be using tail or ...
- 4,656
9
votes
Convert .xyz format to Gaussian Input file (.gjf)
If you have a python installation, you can use ASE to do this in one line.
ase-gui structure.xyz -o structure.gjf
(I have always seen it as gjf not gif)
If you don'...
- 10.7k
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