QM/ELMO: A Multi-Purpose Fully Quantum Mechanical Embedding Scheme Based on Extremely Localized Molecular Orbitals

Abstract

The development of computationally advantageous methods for the study of large systems is a long-standing research topic in theoretical chemistry. Among these techniques, a prominent place is certainly occupied by the multi-scale embedding strategies, from the well-known QM/MM (quantum mechanics / molecular mechanics) methods to the latest and promising fully quantum mechanical approaches. In this Feature Article, we will briefly review the recently proposed QM/ELMO (quantum mechanics / extremely localized molecular orbital) scheme, namely a new multiscale embedding strategy in which the most chemically relevant region of the investigated system is treated at fully quantum chemical level, while the remaining part (namely, the environment) is described by means of transferred extremely localized molecular orbitals that remain frozen throughout the computation. Other than highlighting the theoretical bases, here we will also review the main results obtained through all the currently available variants of the novel method. In particular, we will show how the QM/ELMO embedding scheme has been successfully exploited to perform both ground and excited state calculations, reproducing the results of corresponding fully quantum mechanical computations but with a much lower computational cost. A first application to crystallography will be also discussed and we will describe how the QM/ELMO approach has been recently coupled with the Hirshfeld atom refinement technique to accurately determine the positions of hydrogen atoms from X-ray diffraction data.Given the reliability and quality of the obtained results, future applications of the current versions of the QM/ELMO embedding strategy to different types of chemical problems are to be expected in the near future. Moreover, further algorithmic improvements and methodological developments are also envisaged, such as the development of a polarizable QM/ELMO scheme accounting for the effects of the QM

Three-Layer Multiscale Approach Based on Extremely Localized Molecular Orbitals to Investigate Enzyme Reactions

“…Since this technique has been already introduced and thoroughly described in previous papers, here, we will simply limit to recall its essential features. Interested readers can find more specific details in the Supporting Information or in the seminal works about the QM/ELMO strategy. ,, …”

“…All the QM/ELMO/MM and QM/MM computations were carried out by exploiting our in-house modified version of Gaussian09 that implements the QM/ELMO strategy − and that is coupled with AMBER 2016 for the treatment of the classical terms in eq .…”

“…In line with the strategies just mentioned in the previous paragraph, in this paper, we propose the new three-layer approach QM/ELMO/MM, which results from the combination of our recently developed QM/ELMO technique − with molecular mechanics following a fully Hamiltonian scheme. QM/ELMO is a quantum mechanical embedding method where the most important region of the system can be treated with any traditional approach of quantum chemistry, while the remaining part is described through frozen extremely localized molecular orbitals previously transferred from the above-mentioned ELMO libraries or from suitable model molecules.…”

X-ray restrained extremely localized molecular orbitals for the embedding of quantum mechanical calculations

“…Prompted by this result, we decided to explore the possibility of using pre-determined X-ray restrained extremely localized molecular orbitals (XR-ELMOs) to profitably embed quantum mechanical calculations. To accomplish this task, we exploited the recently developed QM/ELMO (quantum mechanics/extremely localized molecular orbital) embedding approach , 2020, 2021aMacetti et al, , 2021. According to this technique, the chemically active region is treated in a fully quantum mechanical way, while the rest is described by means of transferred and frozen extremely localized molecular orbitals.…”

iOI: an Iterative Orbital Interaction Approach for Solving the Self-Consistent Field Problem

“…As a matter of fact, the best answer to this was already provided by chemists in the early days of chemistry: as the basic building units, functional groups or fragments in general reflect best the locality of chemical systems. As such, various fragment-based quantum chemical methods have been developed in the last decades, including mixed quantum mechanics/molecular mechanics (QM/MM), [4][5][6][7] multilayer QM/QM, [8][9][10][11] divide-and-conquer (DC), [12][13][14][15] embedding, [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] and orbital- [32][33][34][35][36][37][38][39][40][41] and energy-based [42][43][44][45][46][47][48][49][50][51][52]…”