The dissociation energy, equilibrium distance, and spectroscopic constants for the $^1Σ_g^+$ ground state of the Yb$_2$ molecule are calculated. The relativistic effects are introduced through generalized relativistic effective core potentials with very high precision. The scalar relativistic coupled cluster method particularly well suited for closed-shell van-der-Waals systems is used for the correlation treatment. Extensive generalized correlation basis sets were constructed and employed. The relatively small corrections for high-order cluster amplitudes and spin-orbit interactions are taken into account using smaller basis sets and the spin-orbit density functional theory.
Referring to a recent experiment, we theoretically study the process of a two-channel decay of the diatomic silver anion (Ag$_2^-$), namely the spontaneous electron ejection giving Ag$_2$ + e$^-$ and the dissociation leading to Ag$^-$ + Ag. The ground state potential energy curves of the silver molecules of diatomic neutral and negative ion were calculated using proper pseudo-potentials and atomic basis sets. We also estimated the non-adiabatic electronic coupling between the ground state of Ag$_2^-$ and the ground state of Ag$_2$ + e$^-$, which in turn allowed us to estimate the minimal and m…
The vibrational dynamics of formic acid monomer (FAM) and dimer (FAD) is investigated from machine-learned potential energy surfaces at the MP2 (PES$_{\rm MP2}$) and transfer-learned (PES$_{\rm TL}$) to the CCSD(T) levels of theory. The normal modes and anharmonic frequencies of all modes below 2000 cm$^{-1}$ agree favourably with experiment whereas the OH-stretch mode is challenging for FAM and FAD from normal mode analyses and finite-temperature MD simulations. VPT2 calculations on PES$_{\rm TL}$ for FAM reproduce the experimental OH frequency to within 22 cm$^{-1}$. For FAD the VPT2 calcula…
Computational Insights into Mechanostability and Dissociation Dynamics of the Dengue Virus Envelope Protein Ectodomain Dimer Across pH and Temperature Gradients
São Paulo State University (UNESP)（圣保罗州立大学）；Nicolaus Copernicus University in Torun（托伦哥白尼大学）；Istituto Italiano di Tecnologia (IIT)（意大利理工学院）
The advent of ultrashort soft x-ray pulse sources permits the use of established gas phase spectroscopy methods to investigate ultrafast photochemistry in isolated molecules with element and site specificity. In the present study, we simulate excited state wavepacket dynamics of a prototypical process, the ultrafast photodissociation of methyl iodide. Based on the simulation, we calculate time-dependent excited state carbon edge photoelectron and Auger electron spectra. We observe distinct signatures in both types of spectra and show their direct connection to C-I bond dissociation and charge …
Experiments in several intramolecular singlet fission materials have indicated that the triplet-triplet spin biexciton has a much longer lifetime than believed until recently, opening up loss mechanisms that can annihilate the biexciton prior to its dissociation to free triplets. We have performed many-body calculations of excited state wavefunctions of hypothetical phenylene-linked anthracene molecules to better understand linker-dependent behavior of dimers of larger acenes being investigated as potential singlet fission candidates. The calculations reveal unanticipated features that we show…
Simple non-empirical procedure for spin-component-scaled MP2 methods applied to the calculation of dissociation energy curve of noncovalently-interacting systems
The generalized relativistic effective core potential calculations of the adiabatic potential curve and spectroscopic constants for the ground electronic state of the Ca2
Full configuration interaction (FCI) solvers are limited to small basis sets due to their expensive computational costs. An optimal orbital selection for FCI (OptOrbFCI) is proposed to boost the power of existing FCI solvers to pursue the basis set limit under a computational budget. The optimization problem coincides with that of the complete active space SCF method (CASSCF), while OptOrbFCI is algorithmically quite different. OptOrbFCI effectively finds an optimal rotation matrix via solving a constrained optimization problem directly to compress the orbitals of large basis sets to one with …
Time-dependent N-electron valence perturbation theory with matrix product state reference wavefunctions for large active spaces and basis sets: Applications to the chromium dimer and all-trans polyenes
在早期的工作[J. Chem. Phys. 144，064102（2016）]中，我们引入了二阶N电子价态微扰理论（t-NEVPT 2）的时间依赖性公式，其（i）具有比通常的内部收缩微扰公式更低的计算标度，并且（ii）产生完全未收缩的NEVPT 2能量。在这里，我们提出了一个组合的t-NEVPT 2与矩阵产品状态（MPS）的参考波函数（t-MPS-NEVPT 2），允许计算未收缩的动态相关能量为大的活性空间和基组，使用时间相关的密度矩阵重整化群（TD-DMRG）算法。此外，我们报告了一个低尺度的MPS为基础的实施强收缩NEVPT 2（sc-MPS-NEVPT 2），避免了计算的四粒子约简密度矩阵。我们使用这些新的方法来计算的铬二聚体的解离能和研究的低-躺在激发态的全反式多烯（C $_4$ H $_6$ C $_{24}$ H $_{26}$），将动态相关的参考波函数与多达24个活性电子和轨道。
Since the '30s the interatomic potential of the beryllium dimer Be$_2$ has been both an experimental and a theoretical challenge. Calculating the ground-state correlation energy of Be$_2$ along its dissociation path is a difficult problem for theory. We present ab initio many-body perturbation theory calculations of the Be$_2$ interatomic potential using the GW approximation and the Bethe-Salpeter equation (BSE). The ground-state correlation energy is calculated by the trace formula with checks against the adiabatic-connection fluctuation-dissipation theorem formula. We show that inclusion of …
This work concerns \emph{ab initio} calculations of the complete potential energy curve and spectroscopic constants for the ground state $X^1Σ_g^+$ of the beryllium dimer, Be$_2$. High accuracy and reliability of the results is one of the primary goals of the paper. To this end we apply large basis sets of Slater-type orbitals combined with high-level electronic structure methods including triple and quadruple excitations. The effects of the relativity are also fully accounted for in the theoretical description. For the first time the leading-order quantum electrodynamics effects are fully inc…
We investigate the helium dimer in strong magnetic fields, focusing on the spectrum of low-lying electronic states and their dissociation curves, at the full configuration-interaction level of theory. To address the loss of cylindrical symmetry and angular momentum as a good quantum number for nontrivial angles between the bond axis and magnetic field, we introduce the almost quantized angular momentum (AQAM) and show that it provides useful information about states in arbitrary orientations. In general, strong magnetic fields dramatically rearrange the spectrum, with the orbital Zeeman effect…
The Bethe-Salpeter equation (BSE) is the key equation in many-body perturbation theory based on Green's functions to access response properties. Within the $GW$ approximation to the exchange-correlation kernel, the BSE has been successfully applied to several finite and infinite systems. However, it also shows some failures, such as underestimated triplet excitation energies, lack of double excitations, ground-state energy instabilities in the dissociation limit, etc. In this work, we study the performance of the BSE within the $GW$ approximation as well as the $T$-matrix approximation for the…
Singlet fission, a process that splits a singlet exciton into a biexciton, has promise in quantum information. We report time-resolved electron paramagnetic resonance measurements on a molecule, TIPS-BP1$'$, designed to exhibit strongly state-selective relaxation to specific magnetic spin sublevels. The resulting optically pumped "spin polarization" is a nearly pure initial state from the ensemble. The long-lived spin coherences modulate the signal intrinsically, allowing a new measurement scheme that substantially removes noise and uncertainty in the magnetic resonance spectra. A nonadiabatic…
Lifetimes and wave functions of ozone metastable vibrational states near the dissociation limit in full symmetry approach
能量和寿命（宽度）的振动态以上的最低解离极限的$^{16}$ O $_3$使用以前开发的有效的方法，它结合了超球坐标和复杂的吸收势。计算基于最近计算的以光谱精度确定的臭氧的势能面[J. Chem. Phys. { \bf 139}，134307（2013）]。详细讨论了排列对称性对O $_3$的振转动力学和共振态密度的影响。建立了适合于短程和长程部分的振转连续波函数的量子数之间的对应关系。对称性论证表明，由零核自旋玻色子组成的$^{16}$ O $_3$和$^{18}$ O $_3$的允许纯振动（$J=0$）能级不能在基态势能面上离解.计算了臭氧同位素体$^{16}$ O $_3$的束缚态能量和波函数，转动角动量为$J=0$和1，直到离解阈值.对于束缚能级，计算值与实验值吻合较好，振动能的均方根偏差为1~ \cm。转动常数的测定和用于一个简单的识别计算水平的振动模式。
The complex electronic structure and unusual potential energy curve of the chromium dimer have fascinated scientists for decades, with agreement between theory and experiment so far elusive. Here, we present a new ab initio simulation of the potential energy curve and vibrational spectrum that significantly improves on all earlier estimates. Our data support a shift in earlier experimental assignments of a cluster of vibrational frequencies by one quantum number. The new vibrational assignment yields an experimentally derived potential energy curve in quantitative agreement with theory across …
In this work, we report potential energy surfaces (PESs) of the sodium dimer calculated by variational (VMC) and lattice regularized diffusion Monte Carlo (LRDMC). The VMC calculation is accurate for determining the equilibrium distance and the qualitative shape of the experimental PES. Remarkably, after the application of the LRDMC projection to this single determinant ansatz, namely the Jastrow Antisymmetrized Geminal Product (JAGP), chemical accuracy (~ 1kcal/mol) is reached, and the obtained dissociation energy, equilibrium internuclear distance, and harmonic vibrational frequency are in v…
In recent years, machine learning potentials (MLP) for atomistic simulations have attracted a lot of attention in chemistry and materials science. Many new approaches have been developed with the primary aim to transfer the accuracy of electronic structure calculations to large condensed systems containing thousands of atoms. In spite of these advances, the reliability of modern MLPs in reproducing the subtle details of the multi-dimensional potential-energy surface is still difficult to assess for such systems. On the other hand, moderately sized systems enabling the application of tools for …
The charge delocalization error, besides nondynamic correlation, has been a major challenge to density functional theory. Contemporary functionals undershoot the dissociation of symmetric charged dimers A2+, a simple but stringent test, predict a spurious barrier and improperly delocalize charges for charged molecular clusters. We extend a functional designed for nondynamic correlation to treat the charge delocalization error by modifying the nondynamic correlation for parallel spins. The modified functional eliminates those problems and reduces the multielectron self-interaction error. Furthe…
We report state-of-the-art ab initio calculations of the potential energy curve for the $a^3Σ_u^+$ state of the lithium dimer conducted to achieve spectroscopic accuracy ($<$1cm$^{-1}$) without any prior adjustment to fit the corresponding experimental data. The nonrelativistic clamped-nuclei component of the interaction energy is calculated with a composite method involving six-electron coupled cluster and full configuration interaction theories combined with basis sets of Slater-type orbitals ranging in quality from double- to sextuple-zeta. To go beyond the nonrelativistic Born-Oppenheimer …
We present a comprehensive theoretical study of the electronic structures of the Yb atom and the Yb$_2$ molecule, respectively, focusing on their ground and lowest-lying electronically excited states. Our study includes various state-of-the-art quantum chemistry methods such as CCSD, CCSD(T), CASPT2 (including spin--orbit coupling), and EOM-CCSD as well as some recently developed pCCD-based approaches and their extensions to target excited states. Specifically, we scan the lowest-lying potential energy surfaces of the \ce{Yb2} dimer and provide a reliable benchmark set of spectroscopic paramet…
A fully {\it ab initio} potential curve of near-spectroscopic quality for the OH^- anion: importance of connected quadruple excitations and scalar relativistic effects
对羟基阴离子OH ^{-}的基态电势曲线进行了基准研究，包括1粒子和n粒子基组的详细校准。CCSD（T）基组极限高估了$ω_e$约10 cm ^{-1}，这只能通过在耦合团簇展开中包含连接的四重激发--或者等效地，在多参考计算的有效空间中包含$2π$轨道来补救。在包含标量相对论效应（$ω_e$上的~3 cm ^{-1}）后，获得光谱质量（亚cm ^{-1}精度）的势曲线。我们最好的计算EA（OH），1.828 eV，同意小数点后三位的最佳实验值。我们计算的最佳离解能D_0（OH ^-）= 4.7796 eV和D_0（OH）= 4.4124 eV表明实验D_0（OH）= 4.392 eV可能偏低了0.02 eV。
