Abstract
Starting from our recently published implementation of nonadiabatic molecular dynamics (NAMD) on graphics processing units (GPUs), we explore further approaches to accelerate ab initio NAMD calculations at the time-dependent density functional theory (TDDFT) level of theory. We employ (1) the simplified TDDFT schemes of Grimme et al. and (2) the Hammes-Schiffer–Tully approach to obtain nonadiabatic couplings from finite-difference calculations. The resulting scheme delivers an accurate physical picture while virtually eliminating the two computationally most demanding steps of the algorithm. Combined with our GPU-based integral routines for SCF, TDDFT, and TDDFT derivative calculations, NAMD simulations of systems of a few hundreds of atoms at a reasonable time scale become accessible on a single compute node. To demonstrate this and to present a first, illustrative example, we perform TDDFT/MM-NAMD simulations of the rhodopsin protein.
Highlights
Starting from our recently published implementation of nonadiabatic molecular dynamics (NAMD) on graphics processing units (GPUs), we explore further approaches to accelerate ab initio NAMD calculations at the time-dependent density functional theory (TDDFT) level of theory
Nonadiabatic molecular dynamics (NAMD) simulations using trajectory surface hopping (TSH)[1−4] have become a powerful tool to describe the dynamics of molecular systems involving multiple electronic states
Their field of application ranges from the description of rather small molecular machines[5−9] over medium-sized photoswitches[10,11] to the dynamics of entire photoactive proteins.[12,13]. They can be used with a variety of excited-state methods, e.g., the complete active space self-consistent field (CASSCF) method,[14] the algebraic− diagrammatic construction (ADC(2)),[15] several coupled cluster methods (e.g., CC2),[16] as well as time-dependent density functional theory (TDDFT).[17,18]
Summary
P, q, ... are arbitrary molecular orbitals. r is the interatomic distance, η is the mean of the chemical hardness of the atoms N and M. α and β are global fit parameters, while cx is the amount of exact exchange. As a consequence of this, we expect a slight disagreement between the calculated energies and the excited-state properties (ωIx and τ’s) To validate this approach, we compare optimized structures of biphenyl (I) using the S1 potential energy surface at the TDDFT and sTDDFT levels of theory in Table 1 and show ωx’s and τ’s of optimized ground-. We have performed NAMD simulations of II, using the HST model and analytically calculated τ’s as well as RPA, TDA, sRPA, and sTDA. Change of S1 state occupations of protonated formaldimine (II) calculated as an average of all NAMD simulations at (a) the RPA (PBE0/def2-SVP) level of theory using analytical and numerical nonadiabatic couplings and (b) RPA, TDA, sRPA, and sTDA (PBE0/def2-SVP).
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