10 Molecular Properties and Analysis

10.14 General Response Theory

Many of the preceding sections of chapter 10 are concerned with properties that require the solution of underlying equations similar to those from TDDFT (see eq. (7.15)), but in the presence of a (time-dependent) perturbation:

[(𝐀𝐁𝐁*𝐀*)-ωf(𝚺𝚫-𝚫*-𝚺*)](𝐗𝐘)=(𝐕-𝐕*), (10.67)

where 𝚺𝟎 and 𝚫𝟏 for canonical HF/DFT MOs. The functionality for solving these equations with a general choice of operators representing a perturbation 𝐕 is now available in Q-Chem. Both singlet445 and triplet710 response are available for a variety of operators (see table 10.4).

An additional feature of the general response module is its ability to work with non-orthogonal MOs. In a formulation analogous to TDDFT(MI)591, the linear response for molecular interactionsBerquist:2018, or LR(MI), method is available to solve the linear response equations on top of ALMOs.

The response solver can be used with any density functional available in Q-Chem, including range-separated functionals (e.g. CAM-B3LYP, ωB97X) and meta-GGAs (e.g. M06-2X).

There are a few limitations:

  • No post-HF/correlated methods are available yet.

  • Currently, only linear response is implemented.

  • Only calculations on top of restricted and unrestricted (not restricted open-shell) references are implemented.

  • Density functionals including non-local dispersion (e.g. VV10, ωB97M-V) are not yet available.