# Questions tagged [basis-set]

A set of (basis) functions make up a basis set. These functions (generally) represent atomic orbitals whose linear combinations are used to make molecular orbitals (LCAO-MO) in computational chemistry.

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### What are the cheapest basis sets able to model intermolecular dipole interactions inside a metal complex and give good relative energies, with DFT?

As a example, If I have a square planar complex of a cation with both a weakly polar ligand (X) and strongly polar ones, like ammonia and water I expect a bit of stabilization due to formation of a ...
0answers
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### Is this approximate equivalence table between Pople's basis sets and Jensen's DFT attuned polarization consistent basis sets (pcseg-n) correct?

I have some calculations results I runned previously using Pople's basis sets, mostly 6-311+G(d), under Gaussian09. These days I read some texts on Frank Jensen's family of polarization consistent, ...
1answer
392 views

### How to reproduce the Gaussian 09 SDD basis set in Gamess-US?

I'm trying to migrate away from Gaussian 09, using Gamess-US instead for molecular modelling of some heavy alkaline earth metal complexes, using density functional theory (DFT). In some of my previous ...
1answer
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### What is the effect of basis set on charge transfer?

I am calculating the energy and charge transfer of a globally neutral system, composed by two opposely charged monomers (EMIM-BF4), coming closer to each other, with DFT (B3LYP) and MP2. As a thumb ...
0answers
71 views

### Forming Basis Functions from 6-31G Basis Set for Carbon Atom

I am a computer science grad and I am working to write an electronic structure calculation program and I am stuck at forming basis functions using 6-31G Basis set for atoms having higher atomic ...
0answers
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### How to find a full electron basis set that approximate a given ECP basis set?

In computational chemistry of transition metals, there are many popular basis sets, from pople+LANL2DZ mixed basis sets, to Ahlrich and Karlsruhe basis sets like def-SVPD, def2-TZVPPD. Often the ECP ...
1answer
354 views

### Is it good practise to mix double and triple zeta basis sets?

I need to compute extremely accurate single point energies using the coupled cluster method. The methods to be employed scale largely with the number of basis functions. A few basis functions may have ...
1answer
409 views

### Reference on Pople basis set

I need to write reference on 6-311++g(d,p) basis set in my work where I used it on atoms of I-II periods. Does anyone know where it was first published?
0answers
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### What is meaning of LAV2P basis set?

I am working on energy optimization of molecular structure using DFT with SchrĆ¶dinger software and I found that job is running on LAV2P basis set. I want to know what is the meaning of this basis set ...
1answer
130 views

### Optimized General Contractions using the EMSL Basis Set Exchange

When using the EMSL BSE Database and selecting a basis set, one can choose the "Optimized General Contractions" or not. When doing so for, e.g., Nitrogen and the cc-pVDZ some basis functions are not ...
0answers
110 views

### Variational method: Hydrogen atom ground state in STO-3G basis expansion

I computed numerically the ground state energy of hydrogen by variational procedure, firstly expanding the wave function over the s-wave basis set STO-3G $$\psi(r)=\sum_{i=0}^3 C_{i} e^{-\alpha_ir^2}$$...
0answers
227 views

### Hartree Fock for an atom (Beryllium)?

I'm working on solution of Hartree-Fock equation for Beryllium in configuration $1s^2 2s^2$, expanding the orbital with STO-3G basis $$\phi_k=\sum_{p=0}^3 C_{kp}e^{-\alpha_{kp}r^2}$$ I know the values ...
0answers
436 views

### What is the ANO-RCC basis set and how does it work?

On the basis set exchange, the ANO-RCC basis looks huge, even for hydrogen: ...
1answer
6k views

### How many basis functions used in STO-3G and 6-31+G** for the water molecule?

I am a little confused about how to decide how many basis functions that are used in a particular basis set for a given molecule. STO-3G is a so-called "minimal basis set", meaning that only one ...
3answers
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1answer
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### problem with loops over basis sets in psi4 using python

I've recently started using the psi4 quantum chemistry software. I wanted to compare a couple of different basis sets (mainly pople style) on an amino acid. So I've written a python code inside the ...
1answer
2k views

### How to choose the best method and basis set for a calculation in computational chemistry?

In Quantum chemical calculations, it is not always the case that the more complex (correlated) the method or the basis set the more accurate the results. For example, it's sometimes found that MP2 ...
2answers
1k views

### How to compute 2-electron integral for Hartree-Fock code?

I'm working on writing my own code for $\ce{H2}$ in an STO-3G basis set using Hartree-Fock (HF), and I am currently stuck on how to construct the two-electron integral matrix. I know how to evaluate ...
1answer
596 views

### Largest system studied by full CI

What is the largest system (organic molecule) which total energy was calculated by full configuration interaction? Lets say with DZV or similar basis set. How far can we get with CI in larger basis ...
1answer
798 views

### The eigenvector matrix C

I was wondering what the difference between $c_n$ and $c_{jn}$ is? In the context of molecular orbital construction, for example, if $c_{jn}$ is the coefficient of the basis functions $\phi_j$ (...
1answer
151 views

### Are the coefficients and exponents of contracted gaussian same for cartesian and pure form?

The cartesian form of contracted gaussian is something like $$\phi^{CGF}=\sum_{n} s_nx^iy^jz^k \exp(-\alpha_nr^2)$$ and these is also a pure or spherical harmonic version (which I don't know the ...
1answer
870 views

### “NBO diagrams” versus MO diagrams

Molecular orbital diagrams are well known by chemists. According to Wikipedia (emphasis mine), A molecular orbital diagram, or MO diagram, is a qualitative descriptive tool explaining chemical ...
1answer
784 views

### Matching a Slater-type wavefunction with a minimal (STO-nG) Gaussian basis set

I have on hand a high-precision wavefunction expressed in Slater orbitals. I need to express it as accurately as possible in a minimal Gaussian basis set. For background: I am currently working with ...
1answer
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### Accuracy of FP-LAPW vs Plane Wave Pseudopotential: examples

I am trying to learn about FP-LAPW software. I would like to know how well FP-LAPW outperforms Pseudopotential PW calculations. What are some properties/calculations/quantities in which FP-LAPW gives ...
3answers
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### Why are basis sets needed?

I am not sure whether this question is even reasonable, but here it goes. We are taught about the different types of basis sets (extended, minimal, double-zeta, plane wave), but I do not think it is ...
2answers
2k views

### Why are correlation consistent basis sets used with DFT calculations?

Reading some papers, there is a bit of a curious observation that does not exactly make a lot of sense to me. In Quantum Chemistry, different methods exist to carry out geometry optimisation and ...
1answer
855 views

### Why does bond length decrease with increased basis set quality for SCF methods?

From Reviews in Computational Chemistry Vol. 5, for $\ce{H2O}$ using HF, MP2, CCSD, and CCSD(T), all lengths in angstroms:  \small \begin{array}{rcccc} \text{Basis} & \text{HF} & \text{MP2}...
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### Can PBE (and LDA) actually be a better choice sometimes?

Part of my work as an inorganic chemist is to investigate the magnetic coupling between metallic centers in coordination compounds. After some time, I've noticed that the classic PBE functional is the ...
2answers
425 views

### Why large basis sets give better approximations to the exact solution of the Schrödinger equation?

The variational principle states that the energy of any approximate wave function will always be equal to or greater than the energy of the exact solution. Therefore the energy is minimized when ...
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### Which Basis Set is suitable For Mercury-complex in DFT calculations?

Which Basis Set is suitable For Mercury-complex in DFT calculations? Please provide the answers with any journal reference.
1answer
300 views

### An alternative basis set for analytical computation of two electron integrals

It is well known that the usage of the Gaussian basis set, in contrast to Slater basis set, leads relative simple semi-analytical expressions for the two electron repulsion integral $(ab|cd)$. Could ...