The position operator problem in periodic calculations with an emphasis on theoretical spectroscopy

Ditler, Edward; Mattiat, Johann; Luber, Sandra

doi:10.1039/d2cp05991f

Cited by 5 publications

(3 citation statements)

References 184 publications

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“…This behavior is particularly pronounced for liquid water and might arise since the T-EANN model uses the positions relative to the center of mass as input, which are not well-defined in periodic systems. 55,56 Neutral Molecules. The μ of neutral molecules such as H 2 O or (H 2 O) 2 is uniquely defined.…”

Section: Performance Evaluationmentioning

confidence: 99%

“…For the other three systems, including liquid water, the TNEP and SA-GPR models achieve comparable accuracy, while the T-EANN models perform systematically worse. This behavior is particularly pronounced for liquid water and might arise since the T-EANN model uses the positions relative to the center of mass as input, which are not well-defined in periodic systems. , …”

Section: Performance Evaluationmentioning

confidence: 99%

“…Traditional methods for calculating μ cannot be applied to periodic systems since the position operator is not uniquely defined. , This issue is overcome via the modern theory of polarization, ,, which provides a rigorous definition for the polarization of periodic systems and established a methodology for calculating μ . It was therefore used in the present work to obtain μ for periodic systems including water (Sect.…”

Section: Performance Evaluationmentioning

confidence: 99%

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Tensorial Properties via the Neuroevolution Potential Framework: Fast Simulation of Infrared and Raman Spectra

Xu,

Rosander,

Schäfer

et al. 2024

J. Chem. Theory Comput.

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Infrared and Raman spectroscopy are widely used for the characterization of gases, liquids, and solids, as the spectra contain a wealth of information concerning, in particular, the dynamics of these systems. Atomic scale simulations can be used to predict such spectra but are often severely limited due to high computational cost or the need for strong approximations that limit the application range and reliability. Here, we introduce a machine learning (ML) accelerated approach that addresses these shortcomings and provides a significant performance boost in terms of data and computational efficiency compared with earlier ML schemes. To this end, we generalize the neuroevolution potential approach to enable the prediction of rank one and two tensors to obtain the tensorial neuroevolution potential (TNEP) scheme. We apply the resulting framework to construct models for the dipole moment, polarizability, and susceptibility of molecules, liquids, and solids and show that our approach compares favorably with several ML models from the literature with respect to accuracy and computational efficiency. Finally, we demonstrate the application of the TNEP approach to the prediction of infrared and Raman spectra of liquid water, a molecule (PTAF − ), and a prototypical perovskite with strong anharmonicity (BaZrO 3 ). The TNEP approach is implemented in the free and open source software package GPUMD, which makes this methodology readily available to the scientific community.

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Section: Performance Evaluationmentioning

confidence: 99%

Section: Performance Evaluationmentioning

confidence: 99%

Section: Performance Evaluationmentioning

confidence: 99%

See 1 more Smart Citation

Tensorial Properties via the Neuroevolution Potential Framework: Fast Simulation of Infrared and Raman Spectra

Xu,

Rosander,

Schäfer

et al. 2024

J. Chem. Theory Comput.

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Electronic orbital responses of extended systems to static, homogeneous, electromagnetic fields

Springborg,

Kirtman

2024

Chemical Modelling

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We discuss theoretical methods with which the effects of static, homogenous, electromagnetic fields can be determined for systems that are extended and in the ultimate limit are infinite and periodic. We focus here on the finite field (FF) method, but there are obvious implications for perturbation theory approaches as well. The fact that including finite fields in electronic-structure calculations simultaneously introduces the coordinate r→ means that the translational invariance of the potential would be violated and therefore without modification this approach would be inapplicable to infinite, periodic systems. One such long-standing approach is to replace r→ by an operator that involves the derivative with respect to the crystal momentum k→. This is the primary procedure for electrostatic fields. For magnetostatic fields a number of suggestions have been made, all of which are or may be related to changing the gauge used to describe the fields. In the case of a large finite system, for non-vanishing electrostatic and/or magnetostatic field, the lowest energy orbitals are unbound. Thus, the bound states become resonances and the bound-state variational principle can no longer be applied. Instead, special methods for identifying the changes in the system properties due to the presence of these fields are evaluated. Our own simple method based on identifying those orbitals in the field-containing case that are most similar to the occupied orbitals in the field-free case seems to be a promising approach. Since methods for finite molecular systems exposed to static electromagnetic fields are more mature than those for the infinite, periodic crystals, an important issue is to establish that these methods give identical results when treating a crystal as being either large and finite or infinite and periodic. Finally it shall be mentioned that our presentation focuses on methods rather than results. Moreover, it concentrates on our own work that, in some cases, is not yet complete.

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Theory and computation of nuclear shielding

Kupka

2024

Nuclear Magnetic Resonance

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Coupled Cluster approach with singles and doubles and perturbatively included triples, CCSD(T) is still too expensive to model NMR parameters of middle and larger size molecules. Some calculations are additionally improved by inclusion of ro-vibrational (ZPVC), temperature (TC) or relativistic corrections to the results of non-relativistic computations. The progress in theoretical methodology and software will also be briefly mentioned.

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The position operator problem in periodic calculations with an emphasis on theoretical spectroscopy

Abstract: In this article, we present the challenges that arise when carrying out spectroscopic simulations within periodic boundary conditions.

Cited by 5 publications

References 184 publications

Tensorial Properties via the Neuroevolution Potential Framework: Fast Simulation of Infrared and Raman Spectra

Tensorial Properties via the Neuroevolution Potential Framework: Fast Simulation of Infrared and Raman Spectra

Electronic orbital responses of extended systems to static, homogeneous, electromagnetic fields

Theory and computation of nuclear shielding

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