Questions tagged [basis-sets]
For questions about the usage and construction of electronic structure basis sets.
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Choosing the right basis set for describing vdW-interactions with DFT-D3
I want to do some DFT calculations for structures of protonated alkaloid dimers. I know that a method of choice when vdW interactions are involved is the use of dispersion corrections. But now I am ...
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Inputting custom STO-3G basis into PySCF
A simple question about PySCF, but nonetheless I could not find out how to do it: I have a system of atoms for which I already calculated a STO-3G basis in the usual form of MOs:
$$\chi = \sum_i c_i \...
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3
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Can I freeze f functions from a TZ basis set during MP2 (but not during H-F) to speed up calculations?
This is another question about my molecule; as I'm not doing this as an academical affiliate(I'm currently majoring in mathematics), I have only NWChem and my personal laptop on the mix, and thus need ...
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Mixing pseudopotentials with gaussian and plane wave basis
I am somewhat of a novice in computational chemistry of materials, and have been tasked to replicate simulations from a relevant paper. The paper is a bit scant on details so I am trying to recreate ...
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Does the accuracy of RI-MP2 follow the higher number of zetas of the main and fitting bases?
It has been answered to my previous question that RI-MP2/cc-pVTZ/cc-pVTZ gives results of the same quality as MP2/cc-pVTZ. I then started to think about RI-MP2/cc-pVTZ/cc-pVQZ.
The term "basis ...
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Does the RI method actually accelerate basis convergence of MP2, "by one more zeta"?
It is often said that the resolution of the identity (RI) method accelerates the basis set convergence rate of MP2 "by one more zeta", e.g. that RI-MP2/cc-pVTZ/cc-pVTZ results are close to ...
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How does pyscf's internal basis format distinguish between 1s and 2s orbitals?
For example: gto.basis.load("6-31g", "Li") will show:
...
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Do the cc/pc/def2 basis sets mathematically converge to the CBS limit, assuming exact CI/DFT?
The cc-, pc- and def2- basis sets are often described as "systematic", in the sense that the results of these basis sets at different cardinal numbers (i.e. the number of ζ's) can be ...
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Choosing between 6-311++G(3df,3pd) and def2-TZVPPD for certain type of diffuse system
I need to use a diffuse basis set for my highly delocalised molecule, consisting of C, N, O, Cl, S, Mg, Al, B and Si only, since it has many non-covalent interactions inside it. After reading some ...
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Basis Set to analyze a molecule that involves silver
I am a bit new to computational chemistry, but I've been looking into a reaction of a molecule that contains C, H, and F reacting with AgF in a polar solvent. I am looking into one pathway that ...
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How to add different basis sets to different atoms in a calculation (Gaussian 16) when freezing certain atoms?
I am using Gaussian 16 to optimize a paraquat molecule on top of a bulk of gold atoms. Some of these gold atoms are frozen, so I use the option opt=modredundant. I ...
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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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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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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 ...
user4626
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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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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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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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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? [closed]
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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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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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 $2p_x$,
...
- 1,709
11
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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? [closed]
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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