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Purpose of review To summarize the available efficacy and safety data of novel agents for treating acute bacterial skin and skin-structure infections (ABSSSI), focusing on those active against methicillin-resistant Staphylococcus aureus (MRSA). Recent findings There are now several agents active against MRSA that are approved for the treatment of ABSSSI, including tedizolid, ceftaroline, dalbavancin, telavancin, oritavancin, delafloxacin, and omadacycline. In addition, iclaprim has completed phase-3 randomized clinical trials (RCTs). Summary Considering the similar efficacy that arose from direct comparisons in phase-3 RCTs, in order to adopt the best approach for treating ABSSSI on patient-tailored basis, the different safety profiles and formulations of the different available agents should be balanced by taking into account the specific features of each treated patient in terms of baseline comorbidities, related risk of toxicity, need for hospitalization, possibility of early discharge, and expected adherence to outpatient oral therapy.

The role of therapeutic drug monitoring (TDM) of valaciclovir (VA)/aciclovir (A) and valganciclovir/ganciclovir (VG/G) in critically ill patients is still a matter of debate. More data on the dose–concentration relationship might therefore be useful, especially in pediatrics where clinical practice is not adequately supported by robust PK studies. We developed and validated a new liquid chromatography-tandem mass spectrometry (LC-MS/MS) micro-method to simultaneously quantify A and G from plasma and dried plasma spots (DPS). The method was based on rapid organic extraction from DPS and separation on a reversed-phase C-18 UHPLC column after addition of deuterated internal standards. Accurate analyte quantification using SRM detection was then obtained using a Thermo Fisher Quantiva triple-quadrupole MS coupled to an Ultimate 3000 UHPLC. It was validated following international (EMA) guidelines for bioanalytical method validation and was tested on samples from pediatric patients treated with A, VG, or G for cytomegalovirus infection following solid organ or hematopoietic stem cell transplantation. Concentrations obtained from plasma and DPS were compared using Passing–Bablok and Bland–Altman statistical tests. The assay was linear over wide concentration ranges (0.01–20 mg/L) in both plasma and DPS for A and G, suitable for the expected therapeutic ranges for both Cmin and Cmax, accurate, and reproducible in the absence of matrix effects. The results obtained from plasma and DPS were comparable. Using an LC-MS/MS method allowed us to obtain a very specific, sensitive, and rapid quantification of these antiviral drugs starting from very low volumes (50 μL) of plasma samples and DPS. The stability of analytes for at least 30 days allows for cost-effective shipment and storage at room temperature. Our method is suitable for TDM and could be helpful for improving knowledge on PK/PD targets of antivirals in critically ill pediatric patients.

Infections caused by Enterobacterales have become more difficult to treat due to increasing antibiotic resistance, in particular, in the case of production of carbapenemases. Bacterial peritonitis is a common complication of peritoneal dialysis, being Citrobacter spp., an uncommon cause of this syndrome. We report the first case of bacterial peritonitis in continuous ambulatory peritoneal dialysis (CAPD) caused by Citrobacter werkmanii resistant to all beta-lactams, gentamicin, and cotrimoxazole, and also the new anti-gram-negative molecules ceftazidime/avibactam and ceftolozane/tazobactam. The molecular analysis of the strain demonstrated the presence of blaVIM metallo-β-lactamase gene. The patient was effectively cured with a course of systemic tigecycline, colistin, and meropenem.

Objectives: The hypothesis of this study is that tocilizumab should affect common signs of infection due to its immunosuppressive properties. Primary aim of the study was to investigate whether the administration of tocilizumab to critically ill patients with COVID-19, led to a different clinical presentation of infectious complications compared to patients who did not receive tocilizumab. Secondary aim was investigating differences in laboratory parameters between groups. Methods: Single-centre retrospective study, enrolling COVID-19 patients who developed a microbiologically confirmed infectious complication [ventilator associated pneumonia or bloodstream infection] after intensive care unit [ICU] admission and either treated with tocilizumab or not [controls]. Results: A total of 58 patients were included, 25 treated with tocilizumab and 33 controls. Median time from tocilizumab administration to infection onset was 10 days [range 2-26]. Patients were 78% male, with median age 65 years [range 45-79]. At first clinical presentation of the infectious event, the frequency of hypotension [11/25, 44% vs. 11/33, 33%], fever [8/25, 32% vs. 10/33, 30%] or hypothermia [0/25,0%, vs. 2/33, 6%], and oxygen desaturation [6/25, 28% vs 4/33, 12%], as well as the frequency of SOFA score increase of ≥ 2 points [4/25, 16%,vs. 4/33, 12%] was similar in tocilizumab treated patients and controls [p>0.1 for all comparisons]. Among laboratory parameters, C-Reactive Protein elevation was reduced in tocilizumab treated patients compared to controls [8/25, 32% vs. 22/33, 67%, p=0.009]. Conclusion: The clinical features of infectious complications in critically ill patients with COVID-19 admitted to ICU were not affected by tocilizumab.

The aim of the present study is to evaluate if an independent association exists between liver enzyme elevations (LEE) and the risk of mortality or intensive care unit (ICU) admissions in patients with COVID-19. This was a single-center observational study, recruiting all consecutive adults with COVID-19. The elevation of aspartate aminotransferase (AST) or alanine aminotransferase (ALT) to the highest level between COVID-19 diagnosis and hospital discharge was categorized according to a standardized toxicity grade scale. In total, 799 patients were included in this study, 39% of which were female, with a mean age of 69.9 (±16.0) years. Of these patients, 225 (28.1%) developed LEE of grade ≥2 after a median of three days (interquartile range (IQR): 0–8 days) from the diagnosis of COVID-19, and they were estimated to have a higher hazard of death or ICU admission (adjusted hazard ratio (aHR): 1.46, 95% confidence interval (CI): 1.14–1.88). The clinical and laboratory variables associated with the development of LEE were male sex, higher respiratory rate, higher gamma glutamyl transpeptidase (GGT) and lower albumin levels at baseline. Among the analyzed treatments, steroids, tocilizumab and darunavir/ritonavir correlated with LEE. In conclusion, LEE were associated with mortality and ICU admission among COVID-19 patients. While the origin of LEE is probably multifactorial, LEE evaluation could add information to the clinical and laboratory variables that are commonly evaluated during the course of COVID-19.

IntroductionCoronavirus disease 2019 (COVID-19) can lead to respiratory failure due to severe immune response. Treatment targeting this immune response might be beneficial but there is limited evidence on its efficacy.The aim of this study was to determine if early treatment of patients with COVID-19 pneumonia with tocilizumab and/or steroids was associated with better outcome.MethodsThis observational single-center study included patients with COVID-19 pneumonia who were not intubated and received either standard of care (SOC, controls) or SOC plus early (within 3 days from hospital admission) anti-inflammatory treatment. SOC consisted of hydroxychloroquine 400mg bid plus, in those admitted before March 24th, also darunavir/ritonavir. Anti-inflammatory treatment consisted of either tocilizumab (8mg/kg intravenously or 162mg subcutaneously) or methylprednisolone 1 mg/kg for 5 days or both. Failure was defined as intubation or death, and the endpoints were failure-free survival (primary endpoint) and overall survival (secondary) at day 30. Difference between the groups was estimated as Hazard Ratio by a propensity score weighted Cox regression analysis (HROW).ResultsOverall, 196 adults were included in the analyses. They were mainly male (67.4%), with comorbidities (78.1%) and severe COVID-19 pneumonia (83.7%). Median age was 67.9 years (range, 30-100) and median PaO2/FiO2200 mmHg (IQR 133-289). Among them, 130 received early anti-inflammatory treatment with: tocilizumab (n=29, 22.3%), methylprednisolone (n=45, 34.6%), or both (n=56, 43.1%). The adjusted failure-free survival among tocilizumab/methylprednisolone/SOC treated patients vs. SOC was 80.8% (95%CI, 72.8-86.7) vs. 64.1% (95%CI, 51.3-74.0), HROW0.48, 95%CI, 0.23-0.99; p=0.049. The overall survival among tocilizumab/methylprednisolone/SOC patients vs. SOC was 85.9% (95%CI, 80.7-92.6) vs. 71.9% (95%CI, 46-73), HROW0.41, 95%CI: 0.19-0.89, p=0.025.ConclusionEarly adjunctive treatment with tocilizumab, methylprednisolone or both may improve outcomes in non-intubated patients with COVID-19 pneumonia.

International audience; Plasma DNA fragmentomics is an emerging area in cell-free DNA diagnostics and research. In murine models, it has been shown that the extracellular DNase, DNASE1L3, plays a role in the fragmentation of plasma DNA. In humans, DNASE1L3 deficiency causes familial monogenic systemic lupus erythematosus with childhood onset and anti-dsDNA reactivity. In this study, we found that human patients with DNASE1L3 disease-associated gene variations showed aberrations in size and a reduction of a ''CC'' end motif of plasma DNA. Furthermore, we demonstrated that DNA from DNASE1L3-digested cell nuclei showed a median length of 153 bp with CC motif frequencies resembling plasma DNA from healthy individuals. Adeno-associated virus-based transduction of Dnase1l3 into Dnase1l3-deficient mice restored the end motif profiles to those seen in the plasma DNA of wild-type mice. Our findings demonstrate that DNASE1L3 is an important player in the fragmentation of plasma DNA, which appears to act in a cell-extrinsic manner to regulate plasma DNA size and motif frequency.

Background Little is known about the incidence and risk of intensive care unit (ICU)-acquired bloodstream infections (BSI) in critically ill patients with coronavirus disease 2019 (COVID-19). Materials and methods This retrospective, single-centre study was conducted in Northern Italy. The primary study objectives were as follows: (a) to assess the incidence rate of ICU-acquired BSI and (b) to assess the cumulative risk of developing ICU-acquired BSI. Results Overall, 78 critically ill patients with COVID-19 were included in the study. Forty-five episodes of ICU-acquired BSI were registered in 31 patients, with an incidence rate of 47 episodes (95% confidence interval [CI] 35-63) per 1000 patient-days at risk. The estimated cumulative risk of developing at least one BSI episode was of almost 25% after 15 days at risk and possibly surpassing 50% after 30 days at risk. In multivariable analysis, anti-inflammatory treatment was independently associated with the development of BSI (cause-specific hazard ratio [csHR] 1.07 with 95% CI 0.38-3.04 for tocilizumab, csHR 3.95 with 95% CI 1.20-13.03 for methylprednisolone and csHR 10.69 with 95% CI 2.71-42.17 for methylprednisolone plus tocilizumab, with no anti-inflammatory treatment as the reference group; overall P for the dummy variable = 0.003). Conclusions The incidence rate of BSI was high, and the cumulative risk of developing BSI increased with ICU stay. Further study will clarify if the increased risk of BSI we detected in COVID-19 patients treated with anti-inflammatory drugs is outweighed by the benefits of reducing any possible pro-inflammatory dysregulation induced by SARS-CoV-2.

The emerging role of humoral immunity in the pathogenesis of chronic allograft damage has prompted research aimed at assessing the role of anti-HLA antibody (Ab) monitoring as a tool to predict allograft outcome. Data on the natural history of allografts in children developing de novo Ab after transplantation are limited. Utilizing sera collected pretransplant, and serially posttransplant, we retrospectively evaluated 82 consecutive primary pediatric kidney recipients, without pretransplant donor-specific antibodies (DSA), for de novo Ab occurrence, and compared results with clinical-pathologic data. At 4.3-year follow up, 19 patients (23%) developed de novo DSA whereas 24 had de novo non-DSA (NDSA, 29%). DSA appeared at a median time of 24 months after transplantation and were mostly directed to HLA-DQ antigens. Among the 82 patients, eight developed late/chronic active C4d+ antibody-mediated rejection (AMR), and four C4d-negative AMR. Late AMR correlated with DSA (p < 0.01), whose development preceded AMR by 1-year median time. Patients with DSA had a median serum creatinine of 1.44 mg/dL at follow up, significantly higher than NDSA and Ab-negative patients (p < 0.005). In our pediatric cohort, DSA identify patients at risk of renal dysfunction, AMR and graft loss; treatment started at Ab emergence might prevent AMR occurrence and/or progression to graft failure.

The initial synapses of the auditory system, which connect hair cells to afferent nerve fibers, display two unusual features. First, synaptic transmission occurs in a multiquantal fashion: the contents of multiple synaptic vesicles are discharged simultaneously. Second, synaptic transmission may be tuned to specific frequencies of stimulation. We developed a minimal theoretical model to explore the possibility that hair-cell synapses achieve both multiquantal release and frequency selectivity through a cooperative mechanism for the exocytotic release of neurotransmitter. We first characterized vesicle release as a four-step cycle at each release site, then generalized the result to an arbitrary number of steps. The cyclic process itself induces some degree of resonance, and may display a stable, underdamped fixed point of the release dynamics associated with a pair of complex eigenvalues. Cooperativity greatly enhances the frequency selectivity by moving the eigenvalues toward the imaginary axis; spontaneously oscillatory release can arise beyond a Hopf bifurcation. These phenomena occur both in the macroscopic limit, when the number of release sites involved is very large, and in the more realistic stochastic regime, when only a limited number of release sites participate at each synapse. It is thus possible to connect multiquantal release with frequency selectivity through the mechanism of cooperativity.

In the elementary Huckel theory of ground state HF at its simplest valence level the two unknown parameters ∣αp − αh∣ and ∣β∣ can be determined in terms of experimental bond dissociation energy and electric dipole moment. If some sp hybridization is admitted on F in a bond orbital approximation, optimization of the resulting Huckel energy against the hybridization parameter ω using 1-term SCF/STOs shows that little hybridization (ω ≈ 8°) gives a 3% increase in the bond energy parameter ∣β∣ and a 14% reduction in the value of the formal charges ∣δ∣ on the interacting atoms.

Huckel transformation theory is applied to the study of the hybridization problem in ground state NH 3 . Under assumptions similar to those recently introduced for H 2 O, minimization of the model Huckel energy at the valence level yields a trigonometric relation between bond angle and hybridization parameter showing that hybridization opens the interbond angle beyond 90°. A further orthogonal transformation mixing in AOs belonging to A 1 and E symmetry yields four orthogonal sp 3 hybrids of C 3v symmetry on nitrogen that can be engaged in the axially symmetric lone pair and three equivalent straight N–H bonds making the experimental interbond angle.

An orthogonal transformation of the oxygen valence AOs belonging to A 1 symmetry to an ω -hybridized sp basis set allows for useful simplifications reducing Huckel transformed matrix for ground state H 2 O to nearly block-diagonal form. Neglecting delocalization of the hybrid lone pair into the bond, minimization of the resulting Huckel energy shows that for ω ≠ 0 the interbond angle opens beyond 90°. A further orthogonal transformation involving the B 2 y AO yields three orthogonal sp 2 hybrids of C 2v symmetry on oxygen which can be engaged in two equivalent straight O–H bonds making the experimental interbond angle and locally minimizing the Huckel energy of the valence electron configuration.

T-dependent long-range Keesom coefficients are evaluated up to the R-10 term for small values of the dimensionless parameter vertical bar a(ll ')vertical bar For large values of vertical bar all 'vertical bar, I corrections must be introduced mostly for the dipole-dipole term, the correct values of Q being best obtained from a recently derived asymptotic formula. The corresponding attractive energies are the isotropic electrostatic contributions to the interaction energy and are temperature-dependent. Comparison with long-range induction and dispersion energy results for some simple polar axially symmetric molecules in the gas phase shows that at R = 10a(0) and T = 293 K the electrostatic dipole-dipole component is dominant for vertical bar a(11)vertical bar > 0.5. For centrosymmetric molecules the corresponding electrostatic contribution is usually negligible with respect to dispersion.

Explicit analytical formulae are presented for the exact R n -expansion of the short-range electronic interaction energy for ground state H 2 + up to n = 10. The corresponding calculated values for small values of the internuclear distance are in excellent agreement with Peek’s accurate results up to R = 0.30 a 0 .

It is shown in this Letter that the erroneous bond length resulting for the bound 1 Σ u + state of H 2 described by the ionic valence bond structure over the minimum set of 1s STO functions is corrected by the variational inclusion with a substantial weight of the singly excited covalent structures involving 2s and 2pσ STOs onto each H atom. The corresponding value for the molecular energy resulting from the complete optimization of the orbital exponents gives now over 96% of the accurate Kolos–Wolniewicz results.

Frozen-core full-CI calculations of frequency-dependent dipole polarizabilities (FDPs) of ground state BeH 2 at the experimental distance of R = 2.506 a 0 have been performed using an extended set of 208 contracted GTO functions [9s9p5d3f] on Be and [9s8p6d] on H involving about 58 × 10 6 symmetry-adapted Slater determinants. The Casimir–Polder integral was then evaluated analytically using eight optimized imaginary frequencies chosen according to a recently developed interpolation technique which allows for the evaluation of the three dipole dispersion constants for the BeH 2 –BeH 2 homodimer, from which isotropic C 6 and anisotropy γ 6 coefficients are derived for the first time.

Making the usual assumptions typical of elementary Huckel theory including overlap it is shown that the Huckel energy of the two-electron bond is minimized for orbitals having maximum overlap, which yields maximum strength for the straight bond. Analysis of the bond energy for the general A–B bond shows for the molecular orbital description a more complicated dependence on the one-electron exchange-overlap densities of A and B than that recently derived by us in a corresponding valence bond treatment.

Revisitation of the Heitler–London theory for H2 shows that the exchange-overlap component of the bond energy has a strength which is maximum at the bond length. Making the usual assumptions typical of elementary Huckel theory including overlap it is similarly found that in the valence bond description of the chemical bond covalent bonding is strongest for atomic orbitals maximizing the strength of the complete exchange-overlap component of the bond energy.

A two-state model of van der Waals (VdW) interactions is presented which completes the elementary description of the interactions occurring between atoms and molecules. A weak VdW bond is formed between closed-shell atoms or molecules as soon as the small Pauli repulsion is offset in long range by attractive VdW interactions. These are distortion and dispersion interactions, related to the electric properties of the interacting molecules, and described as small second-order effects in terms of long range interaction integrals β s. The explicit forms of these β s are derived from classical electrostatics for atom–atom, atom–linear molecule dispersion, and atom–linear molecule induction. Comparison between C 6 dispersion and induction coefficients for simple homodimers shows that dispersion is, in general, the most important attractive VdW interaction in long range.

The simple Huckel model of the chemical bond, proposed earlier and applied mostly to homonuclear diatomics, is extended to the case of the heteropolar bond. The filling of electrons into the MO levels has now more possibilities than in the previous homonuclear case. For orthogonal AOs, the fundamental quantities entering the model, the atomic energy difference α2−α1 and the bond integral |β| can be determined using the experimental values of the atomization energy De and the electric dipole moment μ. The results obtained for the two-electron σ-bonds occurring in the first-row series of ground state diatomic hydrides are analyzed and shortly discussed.

Fluctuation theory techniques are used to evaluate short-range interactions in ground state H 2 + by calculating in a direct way small energy differences taken with respect to the ground state of the united atom He + . Appropriate coordinate transformation allows to obtain inner and outer Hermitean eigenvalue equations, which are then solved perturbatively in positive powers of the internuclear distance R choosing He + as unperturbed problem. The separation constants are deduced from the regularity conditions on the functions. Next, the function endowed with the right symmetry is constructed by solving an integral equation in a perturbative way. A second-order approximation gives short-range interaction coefficients which are exact up to R 5 .

An elementary technique has been developed to intercept available values of a given atomic or molecular multipole dynamic polarizability through an expression providing a faithful representation for its dependence on the imaginary frequency. The explicitation of the implied interpolative parameters is obtained by imposing that the available data ought to be exactly intercepted. Numerical tests concerning a ground state hydrogen atom have confirmed the reliability of such interpolative procedure for extracting continuous trends from some initial estimates performed on multipole polarizabilities and for evaluating dispersion constants.

Ordinary LCAO-MO theory allows for the ab-initio definition of α and β parameters occurring in the Huckel theory including overlap of simple σ homonuclear systems. One- and two-electron terms not included in Huckel theory are explicitly considered. When such correction terms are neglected in the very spirit of Huckel theory, simple calculation in the hydrogenic approximation for the ground states of H2+, H2, He2+, He2 at the corresponding bond lengths shows semiquantitative agreement with experimental or accurate theoretical results for the bond energies, providing a simple and clear physical picture of the nature of the chemical bond.

DNA binding is crucial to the protective role of the tumor suppressor protein p53, a nuclear phosphoprotein and transcription factor. The mutant human p53 protein S392E is a phosphorylation mimic that has been previously demonstrated to represent an "activated" form of p53 in both in vivo and in vitro assays [Hupp and Lane (1995) J. Biol. Chem. 270, 18165; Hao et al. (1996) J. Biol. Chem. 271, 29380]. Herein, we describe an analysis of structural and functional differences between this mutant and the wild-type protein. Structurally, the S392E protein exhibits increased thermal stability compared to wild-type p53, as monitored by circular dichroism and conformational antibody Ab1620 reactivity. These structural effects include alterations to the core DNA binding domain, remote in sequence space from the site of mutation. Functionally, the S392E mutation does not increase p53 binding to its 20 bp consensus DNA sequence in the absence of nonspecific DNA additives. In contrast, affinity of S392E for a 20 bp nonspecific DNA sequence is enhanced. Embedding 20 bp consensus DNA in the context of longer DNA sequences does not substantially alter S392E affinity, whereas wild-type affinity for these DNAs decreases with increased proportion of nonspecific DNA. These differences may account for the S392E "activated" phenotype and illuminate the role of this modified p53 in vivo.

Small well-shaped basis sets have been used to perform highly accurate variational-perturbative evaluations of dynamic (frequency-dependent) multipole polarizabilities for a hydrogen atom in its ground state. Their structure has been suggested by the ab initio polynomial power expansion we have recently developed to get correspondingly exact results within a finite range covering the region of low frequencies. The frequency-dependent coefficients of the optimized linear combinations of the excited pseudostate orbitals were obtained by diagonalizing the representative matrix of the excitation operator from the ground state. High levels of accuracy have been observed over a set of frequencies now covering the complete real and imaginary ranges.

Full-length human p53 protein was examined using tryptophan fluorescence and circular dichroism spectroscopy (CD) to monitor unfolding. No significant alteration in tryptophan fluorescence for the tetrameric protein was detectable over a wide range of either urea or guanidine hydrochloride concentrations, in contrast to results with the isolated DNA binding domain [Bullock et al. (1997) Proc. Natl. Acad. Sci. USA 94, 14338]. Under similar denaturant conditions, CD demonstrated significant protein unfolding for the full-length wild-type protein, with increased apparent structure loss compared to that detected during thermal denaturation [Nichols and Matthews (2001) Biochemistry 40, 3847]. Examination of X-ray structures containing two of the four tryptophan residues of a p53 monomer suggested local environments consistent with quenched fluorophores. Exploration of p53 fluorescence using potassium iodide as a quencher confirmed that these fluorophores are already substantially quenched in the native structure, and this quenching is not relieved during protein unfolding.

A recently proposed exact power expansion for the dynamic (frequency-dependent) multipole polarizabilities of a ground-state hydrogen atom has been improved keeping its simple polynomial structure substantially unaffected and enlarging its range of convergence. The improvement is performed by adding unexpanded frequency terms taken from the formal expression of the polarizability as a sum-over-states and subtracting their corresponding power expansions. The enlarged range of convergence obtained in this way covers all real frequencies of physical importance and the related imaginary frequencies.

Glucose infusion test: A new screening test for vascular access recirculation. Background Vascular access recirculation is an important cause of diminished dialysis efficiency. We propose a new screening test based on glucose infusion as a tracer for recirculation. Methods The glucose infusion test (GIT) protocol comprises a basal blood sample (A) from the arterial port, a 5 mL bolus of 20% glucose into the venous chamber (time 0), followed by a second sample (B) in four seconds (from 13 to 17 s with Q B 300 mL/min) from the same port. The blood glucose level is determined at the bedside on A and B with a reflectance photometer (CV 1.8%). Interpretation of the test is straightforward: If B=A, there is no recirculation, whereas if B > A, recirculation can be calculated from the regression equation: 0.046 × (B - A) + 0.07, obtained from in vitro tests reproducing artificial recirculation at 0, 5, and 10%. To validate this new method in vivo, we compared GIT and the urea test on 39 hemodialysis patients, obtaining a good correlation ( r = 0.93). The two tests were considered positive (recirculation present) when the lower 95% confidence intervals were more than zero. Results Our patients were divided into two groups: those with (22 out of 39, mean recirculation 11.8%) or without recirculation (17 out of 39, mean 0.06%). The urea test did not recognize 7 out of 22 patients because they had a small recirculation below the urea test limit of detection. Conclusions GIT was more sensitive (detection limit 0.3%), simpler, and immediate in showing the results than the urea test. It is an accurate and low-cost technique for screening and follow-up of vascular access in a dialysis unit.

Long-range dispersion and induction coefficients for the homodimers of Li2, Na2, K2 are evaluated in the LALBM scheme using explicit formulae presented previously and numerical values of moments, polarizabilities and dispersion constants obtained from 2-term reduced spectra of the Kaiserslautern group. While induction coefficients are 5–8 times smaller than dispersion, induction anisotropies are always larger than the corresponding dispersion anisotropies for all homodimers.

Pseudostate decomposition of the first five multipole static polarizabilities of H(1s) obtained from a Givens-Householder diagonalization of (H 0 - EE0) over a N-term STO basis with orbital exponent c = 1 allows for a rapidly convergent evaluation of c 2n dispersion coefficients for H(1s)-H(1s). Twenty-five term pseudospectra with exact ψ0 give C2n values that are accurate to at least 16 significant figures up to 2 n = 14.

The C 8 and C 10 long-range induction coefficients for two like centrosymmetric linear molecules are derived explicitly using the irreducible properties of spherical tensor operators. An application to the H 2 –H 2 system shows that whereas the isotropic induction coefficients are 50–100 times smaller than dispersion, the induction anisotropies γ n are always larger than the corresponding dispersion anisotropies.

The real spherical tensor theory of long-range intermolecular coefficients developed in previous papers is applied to derive explicit formulae for the first three dispersion coefficients for like centrosymmetric linear molecules. The expansion of angledependent coefficients in associated Legendre polynomials allows one to identify the isotropic and anisotropic components of the dispersion interaction in terms of London dispersion constants, the treatment of higher coefficients being simplified by the coupling of the elementary (1, 1′)-polarizations to resultant angular momenta LA and LB onto each molecule. The contributions from all coupling schemes are given explicitly for C6, C8, c10, and numerical results are presented for H2H2 using two-term reduced spectra values from the Kaiserlautern group.

In this chapter we study the regular solutions of the differential equations of quantum mechanics for the free particle, the particle in different boxes, the linear harmonic oscillator, atomic and molecular one-electron systems, the hydrogen atom in a static electric field, and the Stark effect for the hydrogen atom. Through introduction of appropriate separation constants, the partial differential equations resulting for these physical systems are first separated into ordinary one-dimensional differential equations which are then solved by a series expansion in powers of the variable, after the singular points arising in the interval of definition of each variable have been removed by the technique of indicial equations or by studying their asymptotic expansion. The solutions found in this way are then verified by direct substitution of the resulting functions into the original differential equations.

Publisher Summary Calculation of the intermolecular energies from the energy of the whole system A + B, from which subtraction of the energies of the separate molecules is done, meets the enormous difficulties, even at the simplest level. The various difficulties are caused by errors due to: truncation of the basis set, lack of correlation if each molecule is described at the Hartree–Fock level, and basis set superposition. Thus treating the interaction between two molecules as a small perturbation extends the Rayleigh–Schroedinger (RS) perturbation theory to include the exchange and overlap effects in the first order. This chapter discusses the elementary RS perturbation theory by considering the first-order perturbation for the interatomic potential V of the H–H+ and H–H interactions. The chapter also reviews the elements of Murrell–Shaw–Musher–Amos perturbation theory for the interaction among molecules so as to investigate the physical nature of the interaction up to the second order in the intermolecular potential V.

An accurate evaluation of C 6 dispersion coefficients for long-range interactions involving H, He, H 2 + and H 2 has been performed using the London formula in terms of ab initio pseudostate decomposition of the static dipole polarizabilities of the individual atoms and molecules.

Lebeda—Schrader perturbation calculations are performed for ground and excited states of H2 using an Inui ψ0. The first-order function is expanded in a two-centre basis set of linear pseudostates involving powers of spheroidal coordinates and explicitly including the interelectronic distance. Third-order results give errors well below 1% with respect to the corresponding variational values.

Following early work by Kutzelnigg on the correlation cusp, we have attempted to improve convergence of the damped multipole expansion of the second-order induction energy for H+ + by including a separately determined cusp correction of the form φ = f(r B)ψ0 into the first-order function in order to avoid divergency at the proton position when r B = 0. Three different cusp wavefunctions, all derived from the Taylor expansion of f(r B) into positive powers of r B have been examined, and the best compromise between simplicity and accuracy is found for the function φ = -r Bψ0. Few residual multipoles, variationally approximated in terms of one-centre linear pseudostates, are then found necessary to reproduce accurately the induction energy at the distance of the chemical bond.

The two-parameter Inui wavefunction for the ground and excited states of H 2 is improved variationally through an expansion in powers of confocal spheroidal coordinates including the interelectronic distance. A single 69-term expansion gives, for both states, fairly accurate interaction energies in the region of the chemical and van der Waals bond.