Questions tagged [basis-sets]

For questions about the usage and construction of electronic structure basis sets.

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What is the best algorithm for ERIs of contracted gaussian atomic orbitals

I am currently working on python script that does Hartree-Fock-Calculations. I try to avoid packages as good as possible. I've figured out how to calculate the one electron integrals when it comes to ...
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6 votes
1 answer
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How exactly are valence orbitals combined in split valence basis sets such as 3-21G?

For hydrogen, the 3-21G basis set (in CFOUR format) is ...
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How to build cartesian representations of spherical Gaussian basis functions?

I'm trying to code an integral library for my own QC software from scratch. I need to use the spherical basis functions like in any other popular program. So, a D basis function is supposed to make ...
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5 votes
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How are the exponents in a STO-nG basis set obtained?

STO-3G has exponent parameters which can be found in a reference book. Can these parameters be calculated using, for instance, a Hartree–Fock equation for one atom? Or using another way?
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Basis sets optimized for CCSDT(Q) calculations

CCSDT(Q) and CCSDTQ calculations are extraordinarily expensive, both in terms of FLOP count and RAM capacity requirements, eg. CCSDTQ requires a computational effort that scales as ~$N^{10}$, where N ...
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Any molecular codes to calculate non-local susceptibility?

I am interested in calculating the non-interacting non-local susceptibility for simple molecules. In principle, if you have a single Slater determinant, then you should just take a sum over the ...
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5 votes
1 answer
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About the order of indices in basis set expansion

In many books, e.g., Szabo and Ostlund, Helgaker Jorgensen and Olsen, etc etc, the expansion of Hartree-Fock orbital by basis set is written as a kind of $$ \phi_i = \sum_{\mu} C_{\mu i} \chi_{\mu} $$ ...
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9 votes
3 answers
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The number of orbitals in Gaussian/GAMESS log file

After calculating the energy of a $\ce{CH4}$ molecule with a 6-31G(d,p) basis set, I obtained the Gaussian/GAMESS log file and describe a part of the log file as follows. ...
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The format and values provided by Basis Set Exchange

In this question and answers, I found that Basis Set Exchange provides information about the orbitals (e.g., the orbital exponents and contraction coefficients). For example, the following example is ...
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10 votes
4 answers
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How can I find the parameters in a basis set?

I have a question about the basis functions of Gaussian. When the basis function is set (e.g., 6-31G), I would like to know the specific value of Gaussian's parameters for each atom. In particular, I ...
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11 votes
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What is the minimum basis set one should use?

If I'm interested in getting an answer that is minimally correct what is the minimum basis set level I should use? (i.e. anything less would be much less reliable) Obviously this depends on the ...
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How to get energy eigenstates using plane wave basis wavefunction .hdf5 output from Quantum ESPRESSO?

When compiled with the HDF5 flag on, Quantum ESPRESSO (QE) saves wavefunctions in the .save folder. At each k-point, we have an $m\times n$ matrix, where $m$ are the complex number entries of ...
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8 votes
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Difference between original STO-3G and BSE STO-3G

I am trying to work with the STO-3G basis set, but I noticed that the STO-3G in Basis set exchange is different from the STO-3G originally published, and not only that, the BSE version seem to be ...
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Molecular orbitals and active space

During the same minute as asking this question, I also asked this at Quantum Computing SE. In Qiskit, each qubit corresponds to one spin orbital. For example, the $\ce{N2}$ molecule would have 10 ...
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8 votes
2 answers
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Is the number of basis functions same in the different atoms in the 6-31G basis set?

I'm now studying the quantum chemistry calculation and Gaussian basis set. For example, when using the 6-31G basis set, the C atom has 6 basis functions in 1s orbital: 3+1=4 in $2s$, 3+1=4 in $2p_x$, ...
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11 votes
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Critical difference and roles of Slater- and Gaussian-type orbitals

I was very interested in the following question and answer about the Slater- and Gaussian-type orbitals (STO and GTO) used in quantum chemistry and a practical calculation. Gaussian-type orbitals vs ...
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Should augmented basis be used for Hirshfeld charges?

I'm calculating condensed Fukui functions to explain the reactivity of my molecules. The manual for Multiwfn suggests using atomic dipole moment corrected Hirshfeld charges for it. However I get ...
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What quantity to perform CBS extrapolation on for adsorption/binding energies?

When calculating complete basis set extrapolations for quantities, such as adsorption energies or binding energies, which depend on the difference between three quantities (i.e. $E_\textrm{prop} = E_\...
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How to create a differential spectrum from two simulated spectra, calculated by two different basis sets?

In my bachelor thesis, I compare simulated IR-spectra computed by different basis sets. The simulated spectra from sets like cc-pVTZ and cc-pVQZ are too similar to compare them by plotting them next ...
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1 answer
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PES of Tetramethylthiuramdisulfid / Problem with Disulfidbridge

I like to perform a DFT Study on Tetramethylthiuramdisulfid. So I made a structure optimization for my start structur with PW6B95D3/aug-cc-pvtz to get a good structure to begin my dihedral scan to get ...
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Gaussian-type orbitals vs Slater-type orbitals in terms of computational efficiency

When creating molecular orbitals via the linear combination of atomic orbitals method I am told that Slater orbitals provide a more accurate representation whilst Gaussian orbitals are computationally ...
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How are molecular orbitals constructed from the coefficients and basis set?

When an SCF calculation is done in a QM program, the MO coefficients of the solution are printed into the output. Now, graphical softwares can plot 3D molecular orbitals from these coefficients, ...
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14 votes
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What are the physical consequences of adding a constant to the diagonal of the effective Hamiltonian of monolayer materials?

Effective Hamiltonians modeling many-layered materials are often tuned using some sort of bias voltage. For instance, in a $4\times 4$ Hamiltonian matrix to describe biased bilayer graphene using some ...
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17 votes
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How is "basis set projection" done?

I recently came across something called the basis set projection in Q-chem's manual. What it seems to do is to take the converged SCF in a smaller basis set, and then "projects" that onto a ...
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How should I compare different basis sets for post-Hartree-Fock methods?

HF or DFT methods are variational so I can confidently say that any basis set that gives the lowest energy is the best for that system. However, I have learnt that post-HF methods such as MP2, MP3, ...
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11 votes
1 answer
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Is it possible to make segmented contracted basis sets for correlated calculations?

The segmented contracted basis sets are usually handled well by the QM programs than generally contracted basis sets, as the primitives are not repeated. The correlation consistent basis sets (cc-PVnZ)...
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Is basis set superposition error reduced when using the GAPW method?

CP2K implements the Gaussian and Augmented Planewaves (GAPW) approach for all-electron calculations. My understanding is that the GAPW method involves using atom-centered Gaussian type orbitals to ...
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16 votes
2 answers
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What's the best way to compare two DFT codes?

What's the most efficient way to compare the two DFT codes in terms of computation time, basis sets (for example, one plane wave vs one atomic orbitals), functional performance, etc.?
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9 votes
3 answers
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Which software is good with generally contracted basis sets?

Recently, I learnt that basis sets can be contracted as segmented (like def2 or 6-31G) or general (like cc-PVTZ, or ANO). The general contraction allows all the primitives to appear in all shells, ...
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14 votes
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Optimization of Gaussian basis sets within the Hartree-Fock Method

I am revisiting some exercises in Thijssen's Computational Physics book, particularly chapter 4 on the Hartree-Fock method. I am interested in the method of nonlinear optimisation for its own purposes,...
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Which basis set should be used for a system that contains both anions and cations?

I am trying to model a system that has both anions and cations interacting with each other. (In this case it is calcium ion interacting with two small carboxylic acid molecules). Now, looking through ...
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7 votes
2 answers
415 views

p-orbitals in STO-3G basis set

I look at the STO-3G basis set for Carbon atom (downloaded from the basissetexchange.org) and I see one set of exponents and two sets of coefficients for the p-orbitals. How do these exponents and ...
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4 votes
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What are the some other ways to handle BSSE rather than counterpoise correction and using larger basis sets? [closed]

What one can do to eliminate basis set superposition error (BSSE) if there is no chance to use larger basis sets or counterpoise correction.
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442 views

When are atomic-orbital-basis (rather than plane-wave) methods appropriate in periodic DFT?

For example, GPAW supports both plane-wave and atomic-orbital basis methods. I know that atomic-orbital basis methods can have difficulty with electrons occupying vacancies for example, but what ...
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6 votes
1 answer
58 views

Are there properties that can only be calculated with a given set-up?

If you do a bibliography search about the codes used in matter modeling, you will find a large list. I played with a few of them (both free and commercial) and one of my findings is that the ...
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10 votes
1 answer
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How to interpret molden AO/MO coefficients?

A simple calculation with Molpro 2012 on H2 molecule in cc-pvtz basis produces a molden file with 28 molecular orbitals. Each MO is defined with 30 AO/MO coefficient, but the number of symmetric AOs ...
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9 votes
2 answers
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What are the advantages of plane wave basis? [duplicate]

For systems with periodic boundary condition , plane wave basis is usually adopted. While for molecular systems, gaussian basis set is normally adopted. For periodic systems, the gaussian basis is ...
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11 votes
1 answer
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Predicting linear dependencies in a basis set in advance of calculating any integrals

I've been doing some calculations for a water molecule, with a big uncontracted basis set: For oxygen I am using aug-cc-pV9Z supplemented with the "tight" functions from cc-pCV7Z. The s-type exponents ...
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12 votes
2 answers
139 views

Avoiding charge-migration in electronic structure calculations with solvent-like environments

When performing electronic structure calculations on a molecule, one can surround it with point charges to mimic a solvent environment, and lend polarization effects. There is a bit of a caveat ...
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23 votes
1 answer
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Which basis set families were optimized to give the lowest possible variational energy for a given number of orbitals?

Dunning's basis set families (such as cc-pVXZ and aug-cc-pCVXZ) were not optimized to give the lowest variational energy for a given number of orbitals. For example the S-type orbitals are optimized, ...
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17 votes
2 answers
367 views

Understanding the difference between Dunning and Karlsruhe basis sets

I have heard that TURBOMOLE works extremely fast (even compared to MOLPRO) with def2 basis sets, but is slow if Dunning basis sets are used. What is it about def2 basis sets that allows calculations ...
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23 votes
5 answers
490 views

What functions other than Gaussians are used for orbital basis sets?

The Gaussian function $\propto\exp((x-a)^2/b)$ with $b>0$ is one of the most common functions used in molecular modelling (e.g. Gaussian type orbitals). What are some examples of applications of ...
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15 votes
1 answer
214 views

What are good basis sets and functionals for Ni, Cd and Pb?

I will setup a single point energy calculation using Gaussian for a system containing atoms of B-N-Ni, B-N-Pb and B-N-Cd. The system are slabs of boron-nitride [1,2] interacting with those metals. ...
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13 votes
2 answers
299 views

What are the scientific justifications of the binding energy equation?

There are many problems where we want to calculate the binding energy between two systems. Normally, we have a system A, adsorbent (a surface, a nanotube, a protein, etc.), that interact with a system ...
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15 votes
1 answer
102 views

Functionals/basis sets optimized with respect to properties?

In general (at least for molecular calculations) basis sets and DFT functionals are fit to some high level calculation or experimental energy. It is speculated that an accurate energy will result in ...
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27 votes
1 answer
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Approximate equivalence table between Pople's basis sets and Jensen's DFT optimized polarization consistent basis sets (pcseg-n)

At first I posted this question in chemistry.stackexchange.com, before materials.stackexchange.com was launched in beta. As it went unaswered, I'm giving a try here. I have some calculations results ...
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32 votes
3 answers
797 views

What are the positives and negatives of periodic DFT codes that don't use plane-wave basis sets?

Most periodic density functional theory (DFT) codes use plane-wave basis sets in conjunction with three-dimensional periodic boundary conditions. In contrast, for molecular systems of finite size, ...
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16 votes
1 answer
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What methods can be used to calculate excited-states in molecular crystals?

In periodic systems plane-wave basis functions are often used. In a previous question on this site it was questioned if plane-wave basis-sets are reliable for modeling adsorption-processes The ...
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16 votes
1 answer
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How does a complete basis set remove Pulay forces/stress?

When finding nuclear forces for the true electronic wavefunction, thanks to the Hellmann-Feynman theorem we only need to consider explicit derivatives with respect to the nuclear coordinates $\mathbf{...
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18 votes
3 answers
327 views

How trustworthy is the Tran-Blaha modified Becke-Johnson potential and how does it perform across basis sets?

When modeling solid-state materials and particularly semiconductors, one must go beyond LDA and GGA. One alternative is to use hybrid functionals or the $GW$ method. However, this can be very ...
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