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7.11 Correlated Excited State Methods: The ADC(n) Family

7.11.1 Introduction

(February 4, 2022)

The ADC(n) family of correlated excited state methods is a series of size-extensive excited state methods based on perturbation theory. Each order n of ADC presents the excited state equivalent to the well-known nth order Møller-Plesset perturbation theory for the ground state. Currently, the ADC variants ADC(0), ADC(1), ADC(2)-s, ADC(2)-x and ADC(3) are implemented in Q-Chem.1235, 425 The resolution-of-the-identity approximation can be used with any ADC variant. Additionally, there are spin-opposite scaling versions of both ADC(2) variants available.592, 1235 Core-excited states for the simulation of X-ray absorption spectra can be computed exploiting the core-valence separation (CVS) approximation. Currently, the CVS-ADC(1), CVS-ADC(2)-s, CVS-ADC(2)-x and CVS-ADC(3) methods are available.1235, 1198, 1199, 1197 Ionized and electron-attached states can be computed using the non-Dyson IP- and EA-ADC methods. Currently, the IP-ADC(2), IP-ADC(3), EA-ADC(2) and EA-ADC(3) methods are implemented.263, 261, 262, 260