Tuning DTCAM Functionals - Open-Quantum-Platform/openqp GitHub Wiki

[input]
functional=dtcam-tune

[dftgrid]
cam_flag=True
cam_alpha=0.50
cam_beta=-0.20
cam_mu=0.33
hfscale=0.50 can be used as well when cam_flag=False

[tddft]
cam_alpha=0.44
cam_beta=0.22
cam_mu=0.33
hfscale=0.55 can be used as well when cam_flag=False
spc_coco=0.2 ! Spin-pair coupling CO-CO
spc_ovov=0.3 ! Spin-pair coupling OV-OV
spc_coov=0.4 ! Spin-pair coupling CO-OV

A new series of exchange-correlation (XC) functionals have been developed by Qchem Lab at Kyungpook National University, demonstrating exceptional results across various calculations. These functionals are available in Oqua via the following options for functional=:

  • DTCAM-VEE
  • DTCAM-AEE
  • DTCAM-XI
  • DTCAM-XIV
  • DTCAM-VAEE
  • DTCAM-STG

To provide flexibility in tuning the DTCAM-B3LYP functional for optimal results in different calculations, you can select functional=dtcam-tune. This allows customization of the variables in the general formula of these range-separated hybrid functionals.

Formula Explanation

image

  • On the left side of the formula: 1/r_12 This represents the Coulomb potential term, indicating the interaction between two electrons separated by a distance r_12.

  • On the right side: {erf}(\mu_12)

    This is the error function evaluated at mu_{12}, a range-separation parameter. The error function smoothly transitions from 0 to 1, helping to separate the short-range and long-range contributions of the Coulomb potential.

  • The first term represents the short-range part of the interaction.

  • The second term represents the long-range part of the interaction.

Parameters

  • alpha_i: Adjusts the weight of the Hartree-Fock exchange (exact exchange). It is related to the self-consistent field (SCF) part, important for both short-range and long-range components but particularly crucial for the long-range component in the Hartree-Fock exchange.
  • beta_i: Adjusts the weight of the density functional approximation (DFA) part. It affects the response part of the functional, influencing the correlation and exchange-correlation terms. This is more significant for the short-range component where density functional approximations are more effective.

Customization

As demonstrated in the input example, you can easily modify the values of \alpha, \beta, and \mu to achieve the desired combination for your specific calculations.

Spin-Pair Coupling Parameters

The parameters spc_coco, spc_ovov, and spc_coov refer to spin-pair coupling coefficients used in time-dependent density functional theory (TDDFT) calculations. These coefficients adjust the coupling strength between different types of electron pairs, affecting the accuracy of excitation energies and response properties.

  • spc_coco: Adjusts the coupling between pairs of electrons in core orbitals.
  • spc_ovov: Adjusts the coupling between pairs of electrons in occupied and virtual orbitals.
  • spc_coov: Adjusts the coupling between pairs of electrons in core and virtual orbitals.

Hartree-Fock Exchange Scaling (hfscale)

The hfscale parameter determines the proportion of Hartree-Fock exchange included in the hybrid functional calculation.

  • When cam_flag=True:

    • The cam_alpha, cam_beta, and cam_mu parameters control the amount of Hartree-Fock exchange and its separation into short-range and long-range components. In this case, hfscale may not be necessary or is overridden by these parameters.

  • When cam_flag=False:

    • The hfscale parameter is used to set the proportion of Hartree-Fock exchange directly.
    • For example, hfscale=0.55 means that 55% of the exchange interaction is treated using the exact Hartree-Fock method, while the remaining 45% is treated using the density functional approximation (DFA).

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