Two- and one-photon absorption spectra of aqueous thiocyanate anion highlight the role of symmetry in the condensed phase.

We present the two-photon absorption (2PA) spectrum of aqueous thiocyanate calculated using high-level quantum-chemistry methods. The 2PA spectrum is compared to the one-photon absorption (1PA) spectrum computed using the same computational protocol. Although the two spectra probe the same set of electronic states, the intensity patterns are different, leading to an apparent red-shift of the 2PA spectrum relative to the 1PA spectrum. The presented analysis explains the intensity patterns and attributes the differences between the 1PA and 2PA spectra to the native symmetry of isolated SCN - , which influences the spectra in the low-symmetry solvated environment. The native symmetry also manifests itself in variations of the polarization ratio (e.g., parallel vs. perpendicular cross sections) across the spectrum. The presented results highlight the potential of 2PA spectroscopy and high-level quantum-chemistry methods in studies of condensed-phase phenomena.

Method validation, dissipation and residue status of fluopicolide and fosetyl-aluminium in citrus using a rapid extraction method coupled with ultra-performance liquid chromatography-tandem mass spectrometry.

The dissipation and residue status of a combination of fluopicolide and fosetyl-aluminium (fosetyl-Al) in citrus were evaluated in an experimental field. An efficient and sensitive liquid chromatography-tandem mass spectrometry, with rapid extraction, was carried out according to the SANTE guidelines. During the method validation, the recovery was within the range of 106.1-117.5, 94.4-115 and 85.4-109.5%, for fluopicolide, its metabolite 2,6-dichlorobenzamide and fosetyl-Al, respectively, with a relative standard deviation (RSD) of 0.3-10.6%. As a result, accuracy and precision at the spiking concentrations of 0.01, 0.05 and 0.10 mg/kg in citrus were within the acceptable range of 70-120% with an RSD of 20%. The amount of the deposits of fluopicolide, 2,6-dichlorobenzamide and fosetyl-Al was less than the limit of quantification (LOQ) at 0.01 mg/kg at 0 day, adhering to the application in standard [1.77 + 2.66 g of active ingredient (a.i.)/L] and double (3.54 + 5.32 g a.i./L) doses. The present study proposes that the utilisation of fluopicolide and fosetyl-Al in citrus and the soil may not pose a health or environmental hazard provided that good agricultural practices are followed.

Dissipation kinetics of co-formulation with two herbicides, clodinafop-propargyl and oxyfluorfen, in/on onion (Allium cepa) samples.

Supervised field trail on dissipation of co-formulation with herbicides clodinafop-propargyl and oxyfluorfen in spring onion showed similar pattern of dissipation during two different seasons. Residues of clodinafop-propargyl reached ≤ limit of quantitation (LOQ, 0.05 mg kg-1) on 3rd day after application at both standard and double dose during both the seasons. Oxyfluorfen residues followed first-order kinetics in both the doses during first season with half-life of 0.81 to 3.14 days. The residues of clodinafop-propargyl were detected in soil at both the doses during first season. However, residues were ≤ LOQ (0.05 mg kg-1) during second season. The residues of oxyfluorfen were detected only in double dose during first season in soil. In all other cases and in onion bulb, residues were ≤ LOQ (0.05 mg kg-1) at the time of harvest. As the residues were either ≤ LOQ (0.05 mg kg-1) on 3rd day or have a half-life of 3.14 days, the co-formulation can be used safely, provided a pre harvest interval (PHI) of 3 days is followed. On the basis of maximum residue limits (MRLs) in other commodities and from the data of present study, a default MRL of 0.05 mg kg-1 is proposed for both the pesticides.

Theory, implementation, and disappointing results for two-photon absorption cross sections within the doubly electron-attached equation-of-motion coupled-cluster framework.

The equation-of-motion coupled-cluster singles and doubles method with double electron attachment (EOM-DEA-CCSD) is capable of computing reliable energies, wave functions, and first-order properties of excited states in diradicals and polyenes that have a significant doubly excited character with respect to the ground state, without the need for including the computationally expensive triple excitations. Here, we extend the capabilities of the EOM-DEA-CCSD method to the calculations of a multiphoton property, two-photon absorption (2PA) cross sections. Closed-form expressions for the 2PA cross sections are derived within the expectation-value approach using response wave functions. We analyze the performance of this new implementation by comparing the EOM-DEA-CCSD energies and 2PA cross sections with those computed using the CC3 quadratic response theory approach. As benchmark systems, we consider transitions to the states with doubly excited character in twisted ethene and in polyenes, for which EOM-EE-CCSD (EOM-CCSD for excitation energies) performs poorly. The EOM-DEA-CCSD 2PA cross sections are comparable with the CC3 results for twisted ethene; however, the discrepancies between the two methods are large for hexatriene. The observed trends are explained by configurational analysis of the 2PA channels.

Analytical method development, validation and study on behaviour of ipfencarbazone in paddy (rice).

Supervised field trial was conducted to study persistence of a pre-emergent herbicide, ipfencarbazone (25% SC) on rice crop. Single application of two different doses, 156.25 g a.i.ha-1/625 mL formulationha-1 and 312.50 g a.i.ha-1/1250 mL formulationha-1, was applied. Method was validated to analyse ipfencarbazone in rice samples (leaf/plant, grain, straw and husk) and in soil. Initial accumulation of ipfencarbazone in rice plants was 6.72 and 14.71 mg kg-1 in standard and double dose, respectively. The residues decreased linearly with r2 values of 0.92 and 0.98 in different doses and reached below limit of quantitation (LOQ) of 0.01 µg kg-1 (for rice plant/leaf) and 0.05 µg kg-1 (for rice grain, husk, straw) on 30th and 97th (harvest) day respectively after application in both the doses. An average half-life of ipfencarbazone was approximately 4 days. Less than LOQ levels at harvest and short half-life suggest that the use of ipfencarbazone is safe, provided good agricultural practices (GAP) are followed. The data can be used by regulatory authorities like Food Safety and Standards Authority of India (FSSAI) and CODEX for establishing maximum residue limits (MRLs) of ipfencarbazone.

Cherry-Picking Resolvents: Recovering the Valence Contribution in X-ray Two-Photon Absorption within the Core-Valence-Separated Equation-of-Motion Coupled-Cluster Response Theory.

Calculations of first-order response wave functions in the X-ray regime often diverge within correlated frameworks such as equation-of-motion coupled-cluster singles and doubles (EOM-CCSD), a consequence of the coupling with the valence ionization continuum. Here, we extend our strategy of introducing a hierarchy of approximations to the EOM-EE-CCSD resolvent (or, inversely, the model Hamiltonian) involved in the response equations for the calculation of X-ray two-photon absorption (X2PA) cross sections. We exploit the frozen-core core-valence separation (fc-CVS) scheme to first decouple the core and valence Fock spaces, followed by a separate approximate treatment of the valence resolvent. We demonstrate the robust convergence of X-ray response calculations within this framework and compare X2PA spectra of small benchmark molecules with the previously reported density functional theory results.

Probing Molecular Chirality of Ground and Electronically Excited States in the UV-vis and X-ray Regimes: An EOM-CCSD Study.

We present several strategies for computing electronic circular dichroism (CD) spectra across different frequency ranges at the equation-of-motion coupled-cluster singles and doubles level of theory. CD spectra of both ground and electronically excited states are discussed. For selected cases, the approach is compared with coupled-cluster linear response results as well as time-dependent density functional theory. The extension of the theory to include the effect of spin-orbit coupling is presented and illustrated by calculations of X-ray CD spectra at the L-edge.

Persistence evaluation of fluopyram + tebuconazole residues on mango and pomegranate and their risk assessment.

The persistence of combination formulation of fluopyram 200 + tebuconazole 200-400 SC was evaluated across different agro-climates in India for the management of fungal diseases in two commercially important fruit crops, mango and pomegranate. The residues were extracted using quick easy cheap effective rugged and safe (QuEChERS) method and quantification was done on liquid chromatography-tandem mass spectrometry (LC-MS/MS). The fungicide degradation followed 1st-order kinetics and the half-lives were 2.9-6.4 days for mango, and 3.5-7.4 days for pomegranate for both the fungicides. On the basis of Organisation for Economic Co-operation and Development (OECD) maximum residue limit (MRL) calculation, 1.0 mg kg-1 MRL was obtained for fluopyram while for tebuconazole, it was 0.5 mg kg-1 on mango, at the pre-harvest interval (PHI) of 5 days. For pomegranate, the respective MRLs were 1.0 mg kg-1 and 0.7 mg kg-1 at PHI of 7 days. The dietary risk assessment study indicated that % acceptable daily intake (% ADI) and % acute reference dose (% ARfD) were much lower than 100; thus, the application of fluopyram and tebuconazole on mango and pomegranate is unlikely to present public health concern.

Development, validation and evaluation of matrix effect of a QuEChERS-based multiresidue method with low temperature dispersive clean-up for analysis of 104 pesticides in cumin (Cuminum cyminum) by LC-MS/MS.

BACKGROUND: Until now, there is no method available for analysis of pesticide residues in complex matrices like spices. Therefore, there is an urgent need to develop and validate a QuEChERS-based method for the estimation of 104 pesticides in cumin seed. RESULTS: Samples were spiked for 109 pesticides at concentrations of 0.1, 0.5 and 1.0 mg kg-1 . Of these 104 pesticides were recovered. At 0.1, 0.5 and 0.1 mg kg-1 , recoveries ranged from 71% to 108% when compared with matrix matched standards. Seventeen pesticides showed higher or lower recoveries than acceptable range (70-120%) when quantified using solvent standards showing significant matrix effect (ME) (≥ ±20%) even after 20× dilution. However, for the other pesticides ME was significantly eliminated on dilution. The recovery percentage improved for all pesticides on quantitation with matrix matched standards when compared with solvent standards. For pesticides with lower European Union (EU) maximum residue limits (MRLs), an experiment at lower spiking concentrations of 0.01 and 0.05 mg kg-1 with lower dilutions (8×) reveals that almost all pesticides with lower EU MRLs (0.02 and 0.05 mg kg-1 ) showed recoveries in the range 74-124% and relative standard deviation (RSD) less than 20%. CONCLUSION: Theoretical limit of quantitation (LOQ) is proposed which ranged from 0.01 to 0.18 mg kg-1 for matrix matched standards. An LOQ of 0.01 mg kg-1 was easily achieved for the pesticides with lower EU MRLs with lower dilutions (8×) with exception of fipronil for which this can be achieved without dilution provided matrix matched standards are used. The method can be extended to other spices. © 2021 Society of Chemical Industry.

Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package.

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange-correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear-electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an "open teamware" model and an increasingly modular design.

The orbital picture of the first dipole hyperpolarizability from many-body response theory.

We present an approach for obtaining a molecular orbital picture of the first dipole hyperpolarizability (ß) from correlated many-body electronic structure methods. Ab initio calculations of ß rely on quadratic response theory, which recasts the sum-over-all-states expression of ß into a closed-form expression by calculating a handful of first- and second-order response states; for resonantly enhanced ß, damped response theory is used. These response states are then used to construct second-order response reduced one-particle density matrices (1PDMs), which, upon visualization in terms of natural orbitals (NOs), facilitate a rigorous and black-box mapping of the underlying electronic structure with ß. We explain the interpretation of different components of the response 1PDMs and the corresponding NOs within both the undamped and damped response theory framework. We illustrate the utility of this new tool by deconstructing ß for cis-difluoroethene, para-nitroaniline, and hemibonded OH· + H2O complex, computed within the framework of coupled-cluster singles and doubles response theory, in terms of the underlying response 1PDMs and NOs for a range of frequencies.

Use of an Open-Source Software to Examine Low Skeletal Muscle Mass in Penile Cancer Patients: A Cross-Sectional Study.

Purpose: Low skeletal muscle mass determined radiographically has emerged as an important prognostic marker in penile cancer patients but may be unrecognized in obese patients with a high comorbid disease burden. Moreover, publicly available software for image segmentation are limited. Thus, we describe the prevalence of radiographically low skeletal muscle mass in an obese penile cancer cohort, using an open-source software and examine its association with comorbid disease burden. Methods: This is a cross-sectional study, utilizing retrospective data from patients diagnosed with penile squamous cell carcinoma between October 2009 and December 2019. Available digital files of perioperative computerized tomography were analyzed, using CoreSlicer, an open-source image segmentation software. The correlation between radiographically low skeletal muscle mass, defined as a skeletal muscle index (SMI) less than 55 cm2/m2 and a Charlson Comorbidity Index (CCI) greater than 4 was examined, using logistic and linear regression. Results: Forty two of 59 patients had available digital files. Median SMI and body mass index (BMI) were 54.6cm2/m2 and 30.2kg/m2 respectively for the entire cohort. Of included patients, 54% had radiographically low skeletal muscle mass and a median BMI of 28.9 kg/m2. Radiographically low skeletal muscle mass was associated with a CCI greater than 4 on univariable and multivariable logistic regression with odds ratios of 4.85 (p = 0.041) and 7.32 (p = 0.033), respectively. When CCI was treated as a continuous variable on linear regression, the association between radiographically low skeletal muscle mass and CCI was positive, but not statistically significant with an estimated effect of 1.29 (p = 0.1) and 1.27 (p = 0.152) on univariable and multivariable analysis, respectively. Conclusion: Our data demonstrate that low skeletal muscle mass can be readily assessed with CoreSlicer and is associated with a CCI greater than 4 in obese penile cancer patients.

Cherry-picking resolvents: A general strategy for convergent coupled-cluster damped response calculations of core-level spectra.

Damped linear response calculations within the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) framework usually diverge in the x-ray regime. This divergent behavior stems from the valence ionization continuum in which the x-ray response states are embedded. Here, we introduce a general strategy for removing the continuum from the response manifold while preserving important spectral properties of the model Hamiltonian. The strategy is based on decoupling the core and valence Fock spaces using the core-valence separation (CVS) scheme combined with separate (approximate) treatment of the core and valence resolvents. We illustrate this approach with the calculations of resonant inelastic x-ray scattering (RIXS) spectra of benzene and para-nitroaniline using EOM-CCSD wave functions and several choices of resolvents, which differ in their treatment of the valence manifold. The method shows robust convergence and extends the previously introduced CVS-EOM-CCSD RIXS scheme to systems for which valence contributions to the total cross section are important, such as the push-pull chromophores with charge-transfer states.

Correction: How to stay out of trouble in RIXS calculations within equation-of-motion coupled-cluster damped response theory? Safe hitchhiking in the excitation manifold by means of core-valence separation.

Correction for 'How to stay out of trouble in RIXS calculations within equation-of-motion coupled-cluster damped response theory? Safe hitchhiking in the excitation manifold by means of core-valence separation' by Kaushik D. Nanda et al., Phys. Chem. Chem. Phys., 2020, 22, 2629-2641, DOI: .

A simple molecular orbital picture of RIXS distilled from many-body damped response theory.

Ab initio calculations of resonant inelastic x-ray scattering (RIXS) often rely on damped response theory, which prevents the divergence of response solutions in the resonant regime. Within the damped response theory formalism, RIXS moments are expressed as the sum over all electronic states of the system [sum-over-states (SOS) expressions]. By invoking resonance arguments, this expression can be reduced to a few terms, an approximation commonly exploited for the interpretation of computed cross sections. We present an alternative approach: a rigorous formalism for deriving a simple molecular orbital picture of the RIXS process from many-body calculations using the damped response theory. In practical implementations, the SOS expressions of RIXS moments are recast in terms of matrix elements between the zero-order wave functions and first-order frequency-dependent response wave functions of the initial and final states such that the RIXS moments can be evaluated using complex response one-particle transition density matrices (1PTDMs). Visualization of these 1PTDMs connects the RIXS process with the changes in electronic density. We demonstrate that the real and imaginary components of the response 1PTDMs can be interpreted as contributions of the undamped off-resonance and damped near-resonance SOS terms, respectively. By analyzing these 1PTDMs in terms of natural transition orbitals, we derive a rigorous, black-box mapping of the RIXS process into a molecular orbital picture. We illustrate the utility of the new tool by analyzing RIXS transitions in the OH radical, benzene, para-nitroaniline, and 4-amino-4'-nitrostilbene. These examples highlight the significance of both the near-resonance and off-resonance channels.

How to stay out of trouble in RIXS calculations within equation-of-motion coupled-cluster damped response theory? Safe hitchhiking in the excitation manifold by means of core-valence separation.

We present a novel approach for computing resonant inelastic X-ray scattering (RIXS) cross sections within the equation-of-motion coupled-cluster (EOM-CC) framework. The approach is based on recasting the sum-over-states expressions for RIXS moments into closed-form expressions by using damped response theory. Damped response formalism allows one to circumvent problems of divergent behavior of response equations in the resonant regime. However, the convergence of response equations in the X-ray frequency range is often erratic due to the electronically metastable (i.e., resonant) nature of the virtual core-excited states embedded in the valence ionization continuum. We circumvent this problematic behavior by extending the core-valence separation (CVS) scheme, which decouples the valence-excited and core-excited configurations of the excitation manifold, into the response domain. The accuracy of the CVS-enabled damped response theory, implemented within the EOM-EE-CCSD (EOM-CC for excitation energies with single and double excitations) framework, is assessed by comparison against standard damped EOM-EE-CCSD response calculations. The capabilities of the new approach are illustrated by calculations of RIXS cross sections for benzene and benzene radical cation.

The effect of polarizable environment on two-photon absorption cross sections characterized by the equation-of-motion coupled-cluster singles and doubles method combined with the effective fragment potential approach.

We report an extension of a hybrid polarizable embedding method incorporating solvent effects in the calculations of two-photon absorption (2PA) cross sections. We employ the equation-of-motion coupled-cluster singles and doubles method for excitation energies (EOM-EE-CCSD) for the quantum region and the effective fragment potential (EFP) method for the classical region. We also introduce a rigorous metric based on 2PA transition densities for assessing the domain of applicability of QM/MM (quantum mechanics/molecular mechanics) schemes for calculating 2PA cross sections. We investigate the impact of the environment on the 2PA cross sections of low-lying transitions in microhydrated clusters of para-nitroaniline, thymine, and the deprotonated anionic chromophore of photoactive yellow protein (PYPb). We assess the performance of EOM-EE-CCSD/EFP by comparing the 2PA cross sections against full QM calculations as well as against the non-polarizable QM/MM electrostatic embedding approach. We demonstrate that the performance of QM/EFP improves when few explicit solvent molecules are included in the QM subsystem. We correlate the errors in the 2PA cross sections with the errors in the key electronic properties-identified by the analysis of 2PA natural transition orbitals and 2PA transition densities-such as excitation energies, transition moments, and dipole-moment differences between the initial and final states. Finally, using aqueous PYPb, we investigate the convergence of 2PA cross sections to bulk values.

Communication: The pole structure of the dynamical polarizability tensor in equation-of-motion coupled-cluster theory.

In this letter, we investigate the pole structure of dynamical polarizabilities computed within the equation-of-motion coupled-cluster (EOM-CC) theory. We show, both theoretically and numerically, that approximate EOM-CC schemes such as, for example, the EOM-CC singles and doubles model exhibit an incorrect pole structure in which the poles that reflect the excitations from the target state (i.e., the EOM-CC state) are supplemented by artificial poles due to excitations from the CC reference state. These artificial poles can be avoided by skipping the amplitude response and reverting to a sum-over-states formulation. While numerical results are generally in favor of such a solution, its major drawback is that this scheme violates size extensivity.

Validation, residue analysis, and risk assessment of fipronil and flonicamid in cotton (Gossypium sp.) samples and soil.

Cotton crop is highly susceptible to attack by sucking pests. Being an important oilseed and feed crop, it is essential to monitor the pesticides and ensure health protection at consumer level. Therefore, a method was validated to estimate fipronil and flonicamid in various cotton samples and risk assessment was performed. Contamination of oil in the extracts from the various oil seeds and cake samples is a major problem as this oil contaminates the column and interferes with the detection of pesticides. The present manuscript for the first time describes successful analysis of the pesticides from various cotton samples including cotton oil, seed, and cake. Quick, easy, cheap, effective, rugged, and safe (QuEChERS)-based methods were validated for estimation of fipronil and flonicamid in cotton samples and in soil by LC-MS/MS. Recoveries were within the acceptable range of 70-120% with relative standard deviation ≤ 20% and HorRat values < 0.3-1.3. R2 was > 0.99. Matrix effects of 150 and 13.5% were observed for fipronil and flonicamid, respectively, in cotton leaves. Limits of quantitation (LOQs) were in the range of 0.0004 to 0.004 mg kg-1 for fipronil and flonicamid. Cotton samples collected from a field study at different locations were analyzed. Half-life ranged from 2.2 to 5.8 for fipronil and 4.6 to 7.0 days for flonicamid. A pre-harvest interval of 33 days is suggested. The risk assessment studies at maximum residue level values showed HQ < 1 at pre-harvest interval (PHI). The methods being short and easy can be extended to estimate more types of pesticides in different oilseeds. Following a PHI of 33 days, fipronil and flonicamid can be used on cotton at standard dose. As the levels of fipronil and flonicamid were below determination limit in all the soils, the environmental risk is negligible.

Effect of the diradical character on static polarizabilities and two-photon absorption cross sections: A closer look with spin-flip equation-of-motion coupled-cluster singles and doubles method.

We present static polarizabilities and two-photon absorption (2PA) cross sections for the low-lying electronic states of prototypical diradicals such as benzynes and analogues of m-xylylene and p-quinodimethane computed with the spin-flip equation-of-motion coupled-cluster singles and doubles (EOM-SF-CCSD) method. The static polarizabilities were calculated as analytic second derivatives of the EOM energies, and the 2PA cross sections were calculated using the expectation-value approach. We explain the trends in the nonlinear responses of the SF target states by constructing few-states models based on truncated sum-over-states expressions for these nonlinear properties. By using a Huckel-type treatment of the frontier molecular orbitals that host the unpaired electrons, we rationalize the trends in the dipole interactions between the SF target states relevant in the few-states models. We demonstrate the correlation between the nonlinear responses of these electronic states and the diradical character.