DFT Energy - Open-Quantum-Platform/openqp GitHub Wiki

An Examples of a Restricted Hartree-Fock(RHF) DFT Energy calculation

[input]
system=
   8   0.000000000   0.000000000  -0.041061554
   1  -0.533194329   0.533194329  -0.614469223
   1   0.533194329  -0.533194329  -0.614469223
charge=0
runtype=energy
functional=bhhlyp
basis=6-31g*
method=hf

[guess]
type=huckel

[scf]
multiplicity=1
type=rhf

[dftgrid]
rad_type=becke

[input] Section

  • system: This is the coordination of your system, your system's coordination can be achieved through two primary methods for OpenQP. The first method employs the Standard Cartesian format, as illustrated in the provided example. The second method utilizes the .XYZ format. To leverage the .XYZ format, save your coordination details in this format within your input folder, for instance, as H2O.xyz. Subsequently, it can be easily applied by specifying system=H2O.xyz in your input file. Here is an example of .XYZ format:
3
symmetry c1
O        0.000000000      0.000000000     -0.041061554
H       -0.533194329      0.533194329     -0.614469223
H        0.533194329     -0.533194329     -0.614469223

  • charge: The total charge of the system. A value of 0 indicates that the molecule is neutral, with no net charge.

  • runtype: Specifies the type of calculation. energy means that the computation aims to determine the electronic energy of the molecule without performing geometry optimization or calculating properties like gradients or Hessians.

  • basis: The basis set used for the calculation, 6-31gs in this case. The 6-31gs is a split-valence basis set with polarization functions on heavy atoms, designed to provide a good balance between accuracy and computational cost. You can find all of the basis-sets supported by OpenQP within the basis_set folder. Note that the basis-set file names are like 6-31g* -> 6-31g*, 6-31g** -> 6-31g(d,p) so there are no * at all.

  • functional: Specifies the DFT functional to be used. bhhlyp is a hybrid functional that combines Hartree-Fock exchange with B88 exchange and LYP correlation. It's known for its good performance in a variety of systems.

  • method: Indicates that the Hartree-Fock (HF) method will be used. However, the specification of a DFT functional (bhhlyp) suggests that the calculation will incorporate DFT principles, which is indicating a hybrid approach. In practice, HF calculations do not use a functional, so this setup is aim to use RHF as the basis for a DFT calculation, combining the two methodologies.

[guess] Section

  • type: The initial guess for the molecular orbitals. huckel suggests using a simple Hückel molecular orbital (HMO) theory-based guess, which is particularly useful for π-conjugated systems but can serve as a starting point for various molecular systems.

[scf] Section

  • multiplicity: A multiplicity of 1 indicates a singlet state, which is typical for the ground state of closed-shell molecules like water, implying all electrons are paired.

  • type: The rhf (Restricted Hartree-Fock) method is selected for the SCF calculations. RHF is appropriate for singlet state systems and assumes all electrons are spin-paired, providing a wave function that is an eigenfunction of the total spin operator.

image

[dftgrid] Section

  • rad_type: Specifies the becke radial integration scheme for the DFT calculations. The Becke grid is a numerical integration scheme designed to efficiently and accurately integrate the exchange-correlation functional over space, crucial for DFT calculations to approximate electron-electron interactions.

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