Accurate and systematically improvable density functional theory embedding for correlated wavefunctions

Abstract

Articles you may be interested inWe analyze the sources of error in quantum embedding calculations in which an active subsystem is treated using wavefunction methods, and the remainder using density functional theory. We show that the embedding potential felt by the electrons in the active subsystem makes only a small contribution to the error of the method, whereas the error in the nonadditive exchange-correlation energy dominates. We test an MP2 correction for this term and demonstrate that the corrected embedding scheme accurately reproduces wavefunction calculations for a series of chemical reactions. Our projectorbased embedding method uses localized occupied orbitals to partition the system; as with other local correlation methods, abrupt changes in the character of the localized orbitals along a reaction coordinate can lead to discontinuities in the embedded energy, but we show that these discontinuities are small and can be systematically reduced by increasing the size of the active region. Convergence of reaction energies with respect to the size of the active subsystem is shown to be rapid for all cases where the density functional treatment is able to capture the polarization of the environment, even in conjugated systems, and even when the partition cuts across a double bond. © 2014 AIP Publishing LLC.[http://dx

Exact density functional and wave function embedding schemes based on orbital localization

“…In Sec. II A we provide a somewhat different derivation of the projector-based embedding approach of Manby and co-workers, 29,30 which will facilitate the further discussion, and we also present our proposal for the modifications of the theory. In Sec.…”

“…Without orthogonality or in an orbital free representation of the embedding potential, the sum of the subsystem electron densities does not agree with the total density, and the kinetic energy contains a nonadditive term that can be calculated with approximate nonadditive functionals 19,20 or with optimized effective potential methods. [21][22][23][24][25][26][27] Alternative techniques proposed by Rajchel et al 28 and by Manby and co-workers [29][30][31][32] represent the embedded electron density by MOs (approximately) orthogonal to those from which the embedding density is computed. The basic idea is the creation of a Hermitian operator whose eigenfunctions include the embedding and optimized orbitals with different eigenvalues.…”

“…Following the work of Manby and co-workers, 29,30 we suppose that the SCF equations are solved for the entire system with the low-level DFT method defined by E 2 , and the occupied MOs are localized using some localization criterion. For each localized MO (LMO), the atoms are identified on which the orbital is localized, e.g., an atom is assigned to an orbital if the corresponding Mulliken population of the MO is greater than a threshold.…”

Subsystem density-functional theory as an effective tool for modeling ground and excited states, their dynamics and many-body interactions

“…This method, especially when coupled with a correlated wavefunction treatment of the subsystems [65][66][67], has already found important applications [210]. Other types of embedding include the so-called density-matrix embedding methods [211][212][213][214] The subsystem DFT theory of many-body interactions [115] presented in Section 5 has been implemented in the RPA approximation and using only pair-wise terms in the response function perturbative expansion of Eq.…”

Linear-Response Time-Dependent Embedded Mean-Field Theory

“…For example, methods based on localized molecular orbitals lead to complicated implementations for analytical gradients and properties, while many embedding methods place constraints on the subsystem particle numbers, spin state, and spatial extent of the excitation, or they neglect particle-number fluctuations between subsystems, or the environmental response to the excitation. Removing such constraints has motivated the recent development of embedding strategies that are formally exact in the description of subsystem interactions [25][26][27][28][29][30][31][32][33][34][35][36][37] and allow for particle-number fluctuations between subsystems via their description as open quantum systems. [35][36][37] Here, we introduce time-dependent embedded mean-field theory (TD-EMFT), a linear-response approach to describe excited electronic states using the EMFT framework.…”