64 research outputs found
Size dependent electronic properties of silicon quantum dots - an analysis with hybrid, screened hybrid and local density functional theory
We use an efficient projection scheme for the Fock operator to analyze the
size dependence of silicon quantum dots (QDs) electronic properties. We compare
the behavior of hybrid, screened hybrid and local density functionals as a
function of the dot size up to 800 silicon atoms and volume of up to
20nm. This allows comparing the calculations of hybrid and screened
hybrid functionals to experimental results over a wide range of QD sizes. We
demonstrate the size dependent behavior of the band gap, density of states,
ionization potential and HOMO level shift after ionization. Those results are
compared to experiment and to other theoretical approaches, such as
tight-binding, empirical pseudopotentials, TDDFT and GW
The structure and composition statistics of 6A binary and ternary crystalline materials
The fundamental principles underlying the arrangement of elements into solid
compounds with an enormous variety of crystal structures are still largely
unknown. This study presents a general overview of the structure types
appearing in an important subset of the solid compounds, i.e., binary and
ternary compounds of the 6A column oxides, sulfides and selenides. It contains
an analysis of these compounds, including the prevalence of various structure
types, their symmetry properties, compositions, stoichiometries and unit cell
sizes. It is found that these compound families include preferred
stoichiometries and structure types that may reflect both their specific
chemistry and research bias in the available empirical data. Identification of
non-overlapping gaps and missing stoichiometries in these structure populations
may be used as guidance in the search for new materials.Comment: 19 pages, 13 figure
A Qubit-Efficient Variational Selected Configuration-Interaction Method
Finding the ground-state energy of molecules is an important and challenging
computational problem for which quantum computing can potentially find
efficient solutions. The variational quantum eigensolver (VQE) is a quantum
algorithm that tackles the molecular groundstate problem and is regarded as one
of the flagships of quantum computing. Yet, to date, only very small molecules
were computed via VQE, due to high noise levels in current quantum devices.
Here we present an alternative variational quantum scheme that requires
significantly less qubits. The reduction in qubit number allows for shallower
circuits to be sufficient, rendering the method more resistant to noise. The
proposed algorithm, termed variational quantum
selected-configuration-interaction (VQ-SCI), is based on: (a) representing the
target groundstate as a superposition of Slater determinant configurations,
encoded directly upon the quantum computational basis states; and (b) selecting
a-priory only the most dominant configurations. This is demonstrated through a
set of groundstate calculations of the H, LiH, BeH, HO, NH and
CH molecules in the sto-3g basis set, performed on IBM quantum devices.
We show that the VQ-SCI reaches the full-CI (FCI) energy within chemical
accuracy using the lowest number of qubits reported to date. Moreover, when the
SCI matrix is generated ``on the fly", the VQ-SCI requires exponentially less
memory than classical SCI methods. This offers a potential remedy to a severe
memory bottleneck problem in classical SCI calculations. Finally, the proposed
scheme is general and can be straightforwardly applied for finding the
groundstate of any Hermitian matrix, outside the chemical context.Comment: 32 pages, 5 figure
Special considerations in the management of adult patients with acute leukaemias and myeloid neoplasms in the COVID-19 era: recommendations from a panel of international experts
This article is made available for unrestricted research re-use and secondary analysis in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.The ongoing COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 is a global public health crisis. Multiple observations indicate poorer post-infection outcomes for patients with cancer than for the general population. Herein, we highlight the challenges in caring for patients with acute leukaemias and myeloid neoplasms amid the COVID-19 pandemic. We summarise key changes related to service allocation, clinical and supportive care, clinical trial participation, and ethical considerations regarding the use of lifesaving measures for these patients. We recognise that these recommendations might be more applicable to high-income countries and might not be generalisable because of regional differences in health-care infrastructure, individual circumstances, and a complex and highly fluid health-care environment. Despite these limitations, we aim to provide a general framework for the care of patients with acute leukaemias and myeloid neoplasms during the COVID-19 pandemic on the basis of recommendations from international experts
Collectively Induced Quantum-Confined Stark Effect in Monolayers of Molecules Consisting of Polar Repeating Units
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