We present an efficient perturbative method to get the response density matrix using localized non-orthogonal basis sets. This scheme is based on the solution of the coupled perturbed self-consistent ...field equation with the Sternheimer approach, which only requires the occupied states and avoids a sum over unoccupied states. We present a complete derivation of the Sternheimer approach to perturbation theory within the framework of the linear combination of atomic orbitals. To demonstrate the capabilities of this method, we have implemented it in the all-electron Fritz Haber Institute ab initio molecular simulation package and applied it to benchmark molecules. For the response properties with respect to the atomic displacement and to the homogeneous electric field, the results are in excellent agreement with those of the previous traditional method and fully validate this Sternheimer approach.
Raman spectroscopy is an effective tool to analyze the structures of various materials as it provides chemical and compositional information. However, the computation demands for Raman spectra are ...typically significant because quantum perturbation calculations need to be performed beyond ground state calculations. This work introduces a novel route based on deep neural networks (DNNs) and density-functional perturbation theory to access anharmonic Raman spectra for extended systems. Both the dielectric susceptibility and the potential energy surface are trained using DNNs. The ab initio anharmonic vibrational Raman spectra can be reproduced well with machine learning and DNNs. Silicon and paracetamol crystals are used as showcases to demonstrate the computational efficiency.
Within density-functional theory, perturbation theory (PT) is the state-of-the-art formalism for assessing the response to homogeneous electric fields and the associated material properties, e.g., ...polarizabilities, dielectric constants, and Raman intensities. Here, we derive a real-space formulation of PT and present an implementation within the all-electron, numeric atom-centered orbitals electronic structure code FHI-aims that allows for massively parallel calculations. As demonstrated by extensive validation, we achieve a rapid computation of accurate response properties of molecules and solids. As an application showcase, we present harmonic and anharmonic Raman spectra, the latter obtained by combining hundreds of thousands of PT calculations with ab initio molecular dynamics. By using the PBE exchange-correlation functional with many-body van der Waals corrections, we obtain spectra in good agreement with experiment especially with respect to lineshapes for the isolated paracetamol molecule and two polymorphs of the paracetamol crystal.
We present an implementation of the canonical and Laplace-transformed formulation of the second-order Møller–Plesset perturbation theory under periodic boundary conditions using numerical atomic ...orbitals. To validate our approach, we show that our results of the Laplace-transformed MP2 correlation correction for the total energy and the band gap are in excellent agreement with the results of the canonical MP2 formulation. We have calculated the binding energy curve for the stacked trans-polyacetylene at the Hartree–Fock + MP2 level as a preliminary application.
The NAO2GTO scheme provides an efficient way to evaluate the electron repulsion integrals (ERIs) over numerical atomic orbitals (NAOs) with auxiliary Gaussian-type orbitals (GTOs). However, the ...NAO2GTO fitting will significantly impact the accuracy and convergence of hybrid functional calculations. To address this issue, here we propose to use the fitted orbitals as a new numerical basis to properly handle the mismatch between NAOs and fitted GTOs. We present an efficient and linear-scaling implementation of analytical gradients of Hartree-Fock exchange (HFX) energy for periodic HSE06 calculations with fitted NAOs in the HONPAS package. In our implementation, the ERIs and their derivatives for HFX matrix and forces are evaluated analytically with the auxiliary GTOs, while other terms are calculated using numerically discretized GTOs. Several integral screening techniques are employed to reduce the number of required ERI derivatives. We benchmark the accuracy and efficiency of our implementation and demonstrate that our results of lattice constants, bulk moduli, and band gaps of several typical semiconductors are in good agreement with the experimental values. We also show that the calculation of HFX forces based on a master-worker dynamic parallel scheme has a very high efficiency and scales linearly with respect to system size. Finally, we study the geometry optimization and polaron formation due to an excess electron in rutile TiO
by means of HSE06 calculations to further validate the applicability of our implementation.
Quantum Computing is believed to be the ultimate solution for quantum chemistry problems. Before the advent of large-scale, fully fault-tolerant quantum computers, the variational quantum eigensolver ...(VQE) is a promising heuristic quantum algorithm to solve real world quantum chemistry problems on near-term noisy quantum computers. Here we propose a highly parallelizable classical simulator for VQE based on the matrix product state representation of quantum state, which significantly extend the simulation range of the existing simulators. Our simulator seamlessly integrates the quantum circuit evolution into the classical auto-differentiation framework, thus the gradients could be computed efficiently similar to the classical deep neural network, with a scaling that is independent of the number of variational parameters. As applications, we use our simulator to study commonly used small molecules such as HF, HCl, LiH and H
2
O, as well as larger molecules CO
2
, BeH
2
and H
4
with up to
40
qubits. The favorable scaling of our simulator against the number of qubits and the number of parameters could make it an ideal testing ground for near-term quantum algorithms and a perfect benchmarking baseline for oncoming large scale VQE experiments on noisy quantum computers.
Hybrid density-functional calculation is one of the most commonly adopted electronic structure theories in computational chemistry and materials science because of its balance between accuracy and ...computational cost. Recently, we have developed a novel scheme called NAO2GTO to achieve linear scaling (Order-N) calculations for hybrid density-functionals. In our scheme, the most time-consuming step is the calculation of the electron repulsion integrals (ERIs) part, so creating an even distribution of these ERIs in parallel implementation is an issue of particular importance. Here, we present two static scalable distributed algorithms for the ERIs computation. Firstly, the ERIs are distributed over ERIs shell pairs. Secondly, the ERIs are distributed over ERIs shell quartets. In both algorithms, the calculation of ERIs is independent of each other, so the communication time is minimized. We show our speedup results to demonstrate the performance of these static parallel distributed algorithms in the Hefei Order-N packages for ab initio simulations.
V–VI antimony chalcogenide semiconductors have shown exciting potentials for thin film photovoltaic applications. However, their solar cell efficiencies are strongly hampered by anomalously large ...voltage loss (>0.6 V), whose origin remains controversial so far. Herein, by combining ultrafast pump–probe spectroscopy and density functional theory (DFT) calculation, the coupled electronic and structural dynamics leading to excited state self‐trapping in antimony chalcogenides with atomic level characterizations is reported. The electronic dynamics in Sb2Se3 indicates a ≈20 ps barrierless intrinsic self‐trapping, with electron localization and accompanied lattice distortion given by DFT calculations. Furthermore, impulsive vibrational coherences unveil key SbSe vibrational modes and their real‐time interplay that drive initial excited state relaxation and energy dissipation toward stabilized small polaron through electron–phonon and subsequent phonon–phonon coupling. This study's findings provide conclusive evidence of carrier self‐trapping arising from intrinsic lattice anharmonicity and polaronic effect in antimony chalcogenides and a new understanding on the coupled electronic and structural dynamics for redefining excited state properties in soft semiconductor materials.
The excited state properties in soft semiconductor materials could be completely re‐defined by structural dynamics. By combining ultrafast pump–probe spectroscopy, time domain vibrational analysis and theoretical calculations, a new and comprehensive picture of the coupled electronic and anharmonic structural dynamics in photoexcited antimony chalcogenides which leads to carrier self‐trapping and energy loss with atomic level insights is provided.
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