Skip to main content
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 ...
Jack's user avatar
  • 15.2k
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 ...
Nike Dattani - No Free Time's user avatar
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 ...
agaitaarino's user avatar
  • 1,501
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 ...
B. Kelly's user avatar
  • 4,376
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 ...
DoctorSoup's user avatar
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 ...
Camps's user avatar
  • 23.6k
15 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 ...
Tyberius's user avatar
  • 15.6k
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 ...
Tyberius's user avatar
  • 15.6k
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 ...
Camps's user avatar
  • 23.6k
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: "...
Nike Dattani - No Free Time's user avatar
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 ...
Raz Jugovic's user avatar
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 ...
Tyberius's user avatar
  • 15.6k
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 ...
Jon Kragskow's user avatar
11 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 <...
Tyberius's user avatar
  • 15.6k
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 ...
vkj's user avatar
  • 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 ...
Camps's user avatar
  • 23.6k
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 ...
Camps's user avatar
  • 23.6k
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 ...
Susi Lehtola's user avatar
  • 19.7k
10 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 ...
Martin - マーチン's user avatar
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 ...
Tristan Maxson's user avatar
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 ...
Martin - マーチン's user avatar
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&...
Nike Dattani - No Free Time's user avatar
10 votes
Accepted

Compute polarizability after each step of relaxed scan in Gaussian 16

This python script will read the logfile from the scan and generate the corresponding gaussian input files. ...
Hemanth Haridas's user avatar
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 ...
Geoff Hutchison's user avatar
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 ...
Tyberius's user avatar
  • 15.6k
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 ...
S R Maiti's user avatar
  • 7,021
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 ...
Tyberius's user avatar
  • 15.6k
9 votes
Accepted

How to eliminate imaginary frequencies during a Gaussian geometry optimization?

Use tighter convergence criteria. If the geometry is already converged with default convergence criteria, then just using tighter convergence thresholds should work. Look at the tight option in the ...
jheindel's user avatar
  • 3,584
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 ...
Nike Dattani - No Free Time's user avatar
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 ...
Geoff Hutchison's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible