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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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} & ...
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Equivalent of Szabo and Ostlund book for DFT

Szabo and Ostlund book Modern quantum chemistry [1] is extremely useful to understand Hartree-Fock and post-Hartree-Fock methods. Not only it explains the theory behind such methods, but it is also ...
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127 views

How to determine the best computational method for energy calculation of a molecule?

In computational or quantum chemistry text books comparing between various methods for energy calculation of a molecule (e.g geometry optimization) such as Semi-empirical, Ab-initio or DFT and also ...
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240 views

Boys function for Gaussian integrals in ab-initio calculations

A few days ago I mentioned a problem with an Hartree-Fock program I am writing (HF using cartesian Gaussian STO-3G basis set). I can reproduce overlap and kinetic integrals of some references for ...
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167 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 ...
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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 ...
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Computing two-electron integrals with an STO-3G basis set

I am trying to implement a restricted Hartree-Fock calculation using an STO-3G basis set, for fun. I managed to perform this calculation where only $\mathrm{1s}$ orbitals are present ($\ce{H2}$ and ...
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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.
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472 views

Coefficients and Parameters for contracted Gaussian basis sets

I'm trying to write a program to calculate fixed-point Hartree-Fock level energies of molecules (for my amusement) and everything makes sense but this. I've been agonizing over this for almost 3 hours ...
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151 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 ...
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Which computational method/basis set should I use for small molecular ions?

I apologize for a perhaps newbie question. I would like to compute the potential energy surface for several small molecular ions, like $\ce{H2+}$ and $\ce{H3+}$, using quantum chemistry software. ...
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Naming of quantum chemistry basis sets

For some DFT calculations I performed with localized (Gaussian) basis sets, I wonder how the basis sets I used are properly named. The names I could gather are: H, C and O: 6-311G(d,p) Al: 8-511G* ...
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Are Pulay forces expensive to compute?

In a thesis I am reading, it is said that one of the reasons for using plane-wave basis sets for first-principles molecular dynamics (aka ab initio MD) is that the Pulay forces[1,2] that arise from an ...