Hybrid Extended Lagrangian, Post-Hartree–Fock Born–Oppenheimer ab Initio Molecular Dynamics Using Fragment-Based Electronic Structure

Abstract

We present a hybrid ab initio molecular dynamics scheme that includes both DFT and Hartree−Fock-based extended Lagrangian and converged post-Hartree−Fock Born−Oppenheimer components, combined within the framework of a molecular fragmentation-based electronic structure. The specific fragmentation algorithm used here is derived from ONIOM but includes multiple, overlapping "model" systems. The interaction between the various overlapping model systems is approximated by invoking the principle of inclusion−exclusion at the chosen higher level of theory and within a "real" calculation performed at the chosen lower level of theory. Furthermore, here, the lower level electronic structure of the full system is propagated through an extended Lagrangian formalism, whereas the fragments, treated using post-Hartree−Fock electronic structure theories, are computed using the normal converged Born−Oppenheimer treatment. This conservative dynamical approach largely reduces the computational cost to approximate on-the-fly dynamics using post-Hartree−Fock electronic structure techniques and can be very beneficial for large systems where SCF convergence may be challenging and time consuming. Benchmarks are provided for medium-sized protonated water clusters, H 9 O 4 + and H 13 O 6 + , and polypeptide fragments, including a proline tripeptide fragment, and alanine decamer. Structural features are in excellent agreement between the hybrid approach using an MP2:B3LYP fragment-based electronic structure and BOMD using MP2 for the full system. Vibrational properties derived from dynamical correlation functions do show a small redshift for the extended Lagrangian treatments, especially at higher frequencies. Strategies are discussed to improve this redshift. The computational methodology works in parallel using both MPI and OpenMP and shows good scaling with the processor number. The timing benchmarks are provided for the alanine decamer. A powerful feature of the computational implementation is the fact that it is completely decoupled from the electronic structure package being employed and thus allows for an integrated approach that may include several different packages. These computational aspects will be further probed in future publications.

Complete OSV-MP2 Analytical Gradient Theory for Molecular Structure and Dynamics Simulations

“…The trajectory specification of computing RDFs of the O-O and O-H distances was adopted according to the description of Ref. 80 As seen in Figure 4, For instance, the peaks at both low and high frequency regions are relatively intensified by decreasing l osv . On the other hand, a large pair screening appears to substantially weaken the 4000 cm −1 peak at the lower frequency side.…”

Quantum mechanical force fields for condensed phase molecular simulations

“…Whereas LSQMs have been useful for many problems, the efficiency, and in some cases the accuracy of QMFFs have the potential to considerably extend the range of applications, particularly in condensed phase molecular simulations. Fragment-based methods have seen recent use within molecular dynamics simulations, 59,60,109,146,196,197 and to explore the importance of many-body interactions. 53,198 The FMO and mDC methods have been used in drug docking applications of cyclin-dependent kinase 2 inhibitor, 59,199 and to perform PMF profiles of chemical reactions.…”

“…110 ONIOM-based fragmentation algorithms have been applied within a hybrid extended-Lagrangian, post-Hartree-Fock Born-Oppenheimer ab initio molecular dynamics scheme to study protonated water clusters and polypeptide fragments. 196 FMO methods have been further applied using tight-binding models in nonadiabatic dynamics simulations to model charge transfer in the subphtalocyanine(SubPc)/C 60 heterojunction. 212 …”

Embedded, graph‐theoretically defined many‐body approximations for wavefunction‐in‐DFT and DFT‐in‐DFT: Applications to gas‐ and condensed‐phase ab initio molecular dynamics, and potential surfaces for quantum nuclear effects

“…In the process, both extended Lagrangian and Born–Oppenheimer‐based AIMD simulations can be performed at accuracy comparable to coupled cluster singles and doubles (CCSD) and second‐order Møller‐Plesset (MP2) levels of theory with DFT computational cost. [ 39–42 ] Hence, for the first time, in refs. [40,41] we presented Car–Parrinello‐style dynamics, but with CCSD accuracy.…”

“…[ 39–42 ] Hence, for the first time, in refs. [40,41] we presented Car–Parrinello‐style dynamics, but with CCSD accuracy. Similarly, we have shown how multiple graphical representations of molecular systems may be simultaneously utilized to construct accurate potential surfaces in agreement with MP2 and CCSD levels of theory, again at DFT cost.…”