Abstract
The random forest regression (RFR) model was introduced to predict the multiple spin state charges of a heme model, which is important for the molecular dynamic simulation of the spin crossover phenomenon. In this work, a multiple spin state structure data set with 39,368 structures of the simplified heme–oxygen binding model was built from the non-adiabatic dynamic simulation trajectories. The ESP charges of each atom were calculated and used as the real-valued response. The conformational adapted charge model (CAC) of three spin states was constructed by an RFR model using symmetry functions. The results show that our RFR model can effectively predict the on the fly atomic charges with the varying conformations as well as the atomic charge of different spin states in the same conformation, thus achieving the balance of accuracy and efficiency. The average mean absolute error of the predicted charges of each spin state is <0.02 e. The comparison studies on descriptors showed a maximum 0.06 e improvement in prediction of the charge of Fe2+ by using 11 manually selected structural parameters. We hope that this model can not only provide variable parameters for developing the force field of the multi-spin state but also facilitate automation, thus enabling large-scale simulations of atomistic systems.
Highlights
Coordinated compounds of transition metal ions can exhibit a switching phenomenon under certain conditions related to changes in temperature, pressure, light, or magnetic field; the central metal ion changes the spin states, which is the spin transition (ST) or spin crossover (SCO) (Bousseksou et al, 2011; Gutlich et al, 2013)
Further analysis of the charge distribution of different spin states showed that the triplet charge of Fe2+ in most structures was greater than the singlet charge ( 31 > 0, see Figure 4), with the difference being at the highest probability concentrated at 0.1e, while, for the quintuplet and triplet spin state, the difference reached 0.2e
This study aimed at exploring the spin crossover phenomenon in the model heme system according to the characteristics of atomic charge distribution in different spin states with conformation
Summary
Coordinated compounds of transition metal ions can exhibit a switching phenomenon under certain conditions related to changes in temperature, pressure, light, or magnetic field; the central metal ion changes the spin states (the so-called high-spin, HS, and low-spin, LS, configurations), which is the spin transition (ST) or spin crossover (SCO) (Bousseksou et al, 2011; Gutlich et al, 2013). The change of spin state is accompanied by a switch of electron configurations of the central ions, which often leads to marked changes in the physical and chemical properties of the entire complex (Gütlich and Goodwin, 2004; Habenicht and Prezhdo, 2012; Gutlich et al, 2013). Density functional theory (DFT) is the most common choice for routine ground-state calculations; the number of valence electrons scaled cubically, increasing the computational costs significantly (Engler et al, 2019). It will not be suitable, especially when one needs to sample extended size and time scales
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