26 research outputs found
Quasiparticle Levels at Large Interface Systems from Many-body Perturbation Theory: the XAF-GW method
We present a fully ab initio approach based on many-body perturbation theory
in the GW approximation, to compute the quasiparticle levels of large interface
systems without significant covalent interactions between the different
components of the interface. The only assumption in our approach is that the
polarizability matrix (chi) of the interface can be given by the sum of the
polarizability matrices of individual components of the interface. We show
analytically, using a two-state hybridized model, that this assumption is valid
even in the presence of interface hybridization to form bonding and
anti-bonding states, up to first order in the overlap matrix elements involved
in the hybridization. We validate our approach by showing that the band
structure obtained in our method is almost identical to that obtained using a
regular GW calculation for bilayer black phosphorus, where interlayer
hybridization is significant. Significant savings in computational time and
memory are obtained by computing chi only for the smallest sub-unit cell of
each component, and expanding (unfolding) the chi matrix to that in the unit
cell of the interface. To treat interface hybridization, the full wavefunctions
of the interface are used in computing the self-energy. We thus call the method
XAF-GW (X: eXpand-chi, A: Add-chi, F: Full wavefunctions). Compared to
GW-embedding type approaches in the literature, the XAF-GW approach is not
limited to specific screening environments or to non-hybridized interface
systems. XAF-GW can also be applied to systems with different dimensionalities,
as well as to Moire superlattices such as in twisted bilayers. We illustrate
the generality and usefulness of our approach by applying it to self-assembled
PTCDA monolayers on Au(111) and Ag(111), and PTCDA monolayers on
graphite-supported monolayer WSe2, where good agreement with experiment is
obtained.Comment: More detailed proof of Add-Chi for hybridized states added in this
versio
Dielectric Screening by 2D Substrates
Two-dimensional (2D) materials are increasingly being used as active
components in nanoscale devices. Many interesting properties of 2D materials
stem from the reduced and highly non-local electronic screening in two
dimensions. While electronic screening within 2D materials has been studied
extensively, the question still remains of how 2D substrates screen charge
perturbations or electronic excitations adjacent to them. Thickness-dependent
dielectric screening properties have recently been studied using electrostatic
force microscopy (EFM) experiments. However, it was suggested that some of the
thickness-dependent trends were due to extrinsic effects. Similarly, Kelvin
probe measurements (KPM) indicate that charge fluctuations are reduced when BN
slabs are placed on SiO, but it is unclear if this effect is due to
intrinsic screening from BN. In this work, we use first principles calculations
to study the fully non-local dielectric screening properties of 2D material
substrates. Our simulations give results in good qualitative agreement with
those from EFM experiments, for hexagonal boron nitride (BN), graphene and
MoS, indicating that the experimentally observed thickness-dependent
screening effects are intrinsic to the 2D materials. We further investigate
explicitly the role of BN in lowering charge potential fluctuations arising
from charge impurities on an underlying SiO substrate, as observed in the
KPM experiments. 2D material substrates can also dramatically change the
HOMO-LUMO gaps of adsorbates, especially for small molecules, such as benzene.
We propose a reliable and very quick method to predict the HOMO-LUMO gap of
small physisorbed molecules on 2D and 3D substrates, using only the band gap of
the substrate and the gas phase gap of the molecule.Comment: 24 pages, 5 figures, Supplementary Informatio
Bulk Photovoltaics in Nanoscale Systems -- Origin of Shift Currents in the Many-Body Picture
The shift current in bulk photovoltaics is commonly attributed to a shift in
non-interacting charge centres. We show that the origin of shift currents in
the many-body picture is fundamentally different. Here the shift current arises
largely from a many-body shift vector that also involves shifts in charge
centres, but these are associated with pairs of nearly-degenerate excitons
overlapping in k-space. The shift current can thus be enhanced by
nearly-degenerate, optically-active and tightly-bound excitons, spread out in
k-space. Ab initio results are presented for BaTiO, NbOCl and MoS
Associations of dietary factors with gastric cancer risk: insights from NHANES 2003–2016 and mendelian randomization analyses
Background: Gastric cancer (GC) continues to be one of the leading causes of cancer-related deaths globally. Diet significantly influences the incidence and progression of GC. However, the relationship between dietary intake and GC is inconsistent.Methods: A study was conducted with adults who participated in the National Health and Nutrition Examination Survey (NHANES) from 2003 to 2016 to investigate possible associations between 32 dietary factors and GC. To further detect potential causal relationships between these dietary factors and the risk of GC, a two-sample Mendelian randomization (MR) analysis was conducted. The primary method employed was the inverse variance weighted (IVW) analysis, and its results were further validated by four other methods.Results: Of the 35,098 participants surveyed, 20 had a history of GC. Based on the results of weighted logistic multivariate analysis, it was observed that there was a positive correlation between total fat intake [odds ratio (OR) = 1.09, 95% confidence interval (CI): (1.01–1.17), p = 0.03] and GC as well as negative association of dietary monounsaturated fatty acids (MUFAs) intake [OR = 0.83, 95% CI: (0.76–0.92), p < 0.001]. Further evaluations of the odds of GC across the quartiles of dietary MUFAs showed that the top quartile of total MUFA intake was associated with a lower likelihood of GC in three different models [model1: OR = 0.03, 95% CI: (0.00–0.25), p < 0.01; model2: OR = 0.04, 95% CI: (0.00–0.38), p = 0.01; model3: OR = 0.04, 95% CI: (0.00–0.40), p = 0.01]. For the MR analyses, genetic instruments were selected from the IEU Open GWAS project; IVW analysis showed that GC risk was not associated with MUFAs [OR = 0.82, 95% CI: (0.59–1.14), p = 0.23] or the ratio of MUFAs to total fatty acids [OR = 1.00, 95% CI: (0.75–1.35), p = 0.98]. Similar results were observed when using the other MR methods.Conclusion: The NHANES study revealed that consuming MUFAs was linked to a lower risk of GC, although the results of MR analyses do not provide evidence of a causal relationship. Additional research is therefore necessary to clarify these findings
Laparoscopic distal gastrectomy demonstrates acceptable outcomes regarding complications compared to open surgery for gastric cancer patients with pylorus outlet obstruction
BackgroundFor gastric cancer (GC) patients with pylorus outlet obstruction (POO), whether laparoscopic surgery has advantages over open surgery remains unclear. This study aims to investigate the differences between patients with and without POO in open and laparoscopic groups and to determine the differences between laparoscopic distal gastrectomy (LDG) and open distal gastrectomy (ODG) in GC patients with POO.MethodsA total of 241 GC patients with POO who underwent distal gastrectomy at the Department of Gastric Surgery of the First Affiliated Hospital of Nanjing Medical University between 2016 and 2021 were included in this study. A total of 1,121 non-POO patients who underwent laparoscopic surgery and 948 non-POO patients who underwent open surgery from 2016 to 2021 were also enrolled in the study. We compared complication rates and hospital stays between open and laparoscopic groups.ResultsThere was no significant difference for LDG between GC patients with and without POO regarding the overall complication rates (P = 0.063), the Grade III–V complication rate (P = 0.673), and the anastomotic complication rate (P = 0.497) from 2016 to 2021. The patients with POO had longer preoperative hospital stay (P = 0.001) and postoperative hospital stay (P=0.007) compared to patients without POO. No significant difference was observed for open patients between POO and non-POO patients regarding the overall complication rate (P = 0.357), grade III–V complication rate (P = 1.000), and anastomosis-related complication rate (P = 0.766). Compared with open surgery in GC patients with POO (n = 111), the total complication rate of the LDG group was 16.2%, which was significantly lower than that of the open group (26.1%, P = 0.041). No significant differences in the Grade III–V complication rate (P = 0.574) and anastomotic complication rate (P = 0.587) were observed between laparoscopic and open groups. Patients receiving laparoscopic surgery had shorter postoperative hospital stay than open surgery (P = 0.001). More resected lymph nodes (LNs) were also observed in the laparoscopic group (P = 0.0145).ConclusionThe comorbidity of GC with POO does not increase the complication rate after laparoscopic or open distal gastrectomy. In GC patients with POO, laparoscopic surgery shows advantages over open surgery with a lower overall complication rate, shorter postoperative hospital stay, and more harvested lymph nodes. Laparoscopic surgery is a safe, feasible, and effective treatment for GC with POO
Theoretical studies of the electromagnetic response of metal nanoparticles
My PhD project aims at developing a set of theoretical models to explain the electromagnetic response of metal nanoparticles, ranging from sub-nanometer to hundreds of nanometers and bulk. Simple metals such as sodium and lithium serve to define the zeroth order approximation. The next step will be to consider particular role of d-electrons in noble metal and how it can be modeled while keeping the optical response driven fully by delocalized valence electrons. We introduce a modified Random Phase Approximation with exact Exchange. The jellium background of Ag cores is treated as a polarizable sphere, which screens the dipole component of the electron-electron interaction. Our model gives the blue shift as cluster size decreases for cationic Ag clusters which agrees well with experimental data. For clusters embedded in rare-gas matrix, we propose a similar polarization screening model. The dipole surface resonance peak is shifted to lower energy significantly.Doctor of Philosophy (IGS
Medium-induced change of the optical response of metal clusters in rare-gas matrices
Interaction with the surrounding medium modifies the optical response of embedded metal clusters. For clusters from about ten to a few hundreds of silver atoms, embedded in rare-gas matrices, we study the environment effect within the matrix random phase approximation with exact exchange (RPAE) quantum approach, which has proved successful for free silver clusters. The polarizable surrounding medium screens the residual two-body RPAE interaction, adds a polarization term to the one-body potential, and shifts the vacuum energy of the active delocalized valence electrons. Within this model, we calculate the dipole oscillator strength distribution for Ag clusters embedded in helium droplets, neon, argon, krypton, and xenon matrices. The main contribution to the dipole surface plasmon red shift originates from the rare-gas polarization screening of the two-body interaction. The large size limit of the dipole surface plasmon agrees well with the classical prediction.Published versio
Medium-induced change of the optical response of metal clusters in rare-gas matrices
10.1103/PhysRevA.96.043404PHYSICAL REVIEW A96
Core-polarization-corrected random-phase approximation with exact exchange for dipole surface plasmons in silver clusters
10.1103/PhysRevA.94.043415PHYSICAL REVIEW A94
Valley Zeeman effect and Landau levels in two-dimensional transition metal dichalcogenides
10.1103/physrevresearch.2.033256Physical Review Research23033256