Hasil untuk "physics.comp-ph"

Yiran Bai, Feng Xiong, Xueheng Kuang

Classical computation of electronic properties in large-scale materials remains challenging. Quantum computation has the potential to offer advantages in memory footprint and computational scaling. However, general and practical quantum algorithms for simulating large-scale materials are still lacking. We propose and implement random-state quantum algorithms to calculate electronic-structure properties of real materials. Using a random state circuit with only a few qubits, we employ real-time evolution with first-order Trotter decomposition and Hadamard test to obtain electronic density of states, and we develop a modified quantum phase estimation algorithm to calculate real-space local density of states via direct quantum measurements. Furthermore, we validate these algorithms by numerically computing the density of states and spatial distributions of electronic states in graphene, twisted bilayer graphene quasicrystals, and fractal lattices, covering system sizes from hundreds to thousands of atoms. Our results manifest that the random-state quantum algorithms provide a general and qubit-efficient route to simulating electronic properties of large-scale periodic and aperiodic materials on quantum computers.

Chuang-Chao Ye, Ning-Bo An, Teng-Yang Ma et al.

Great progress has been made in quantum computing in recent years, providing opportunities to overcome computation resource poverty in many scientific computations like computational fluid dynamics (CFD). In this work, efforts are made to exploit quantum potentialities in CFD, and a hybrid classical and quantum computing CFD framework is proposed to release the power of current quantum computing. In this framework, the traditional CFD solvers are coupled with quantum linear algebra libraries in weak form to achieve collaborative computation between classical and quantum computing. The quantum linear solver provides high-precision solutions and scalable problem sizes for linear systems and is designed to be easily callable for solving linear algebra systems similar to classical linear libraries, thus enabling seamless integration into existing CFD solvers. Some typical cases are performed to validate the feasibility of the proposed framework and the correctness of quantum linear algorithms in CFD.

Wouter Deleersnyder, Evert Slob

Full 3D modelling of time-domain electromagnetic data requires tremendous computational resources. Consequently, simplified physics models prevail in geophysics, using a much faster but approximate (1D) forward model. We propose to join the accuracy of a 1D simplified physics model with the flexibility of coarse grids to reduce the modelling errors, thereby avoiding the full 3D accurate simulations. We exemplify our approach on airborne time-domain electromagnetic data, comparing the modelling error with the standard 3% measurement noise. We find that the modelling error depends on the specific subsurface model (electrical conductivity values, angle representing the deviation of the 1D assumption) and the specific (temporal) discretization. In our example, the computation time is decreased by a factor of 27. Our approach can offer an alternative for surrogate models, statistical relations derived from large 3D datasets, to replace the full 3D simulations.

Anna Sitek, Kristinn Torfason, Andrei Manolescu et al.

We perform a computational study, based on the molecular dynamics method, of the shape of Miram curves obtained from microscale planar diodes. We discuss the smooth transition from the source-limited to space-charge-limited regime due to the finite size of the emitter, i.e. the "knee" in the Miram curve. In our model we find that the smoothing occurs mostly due to the increased emission at the external edges of the emitting area, and that the knee becomes softer when the size of the emitting area decreases. We relate this to the recent work which has described how a heterogeneous work function similarly affects the Miram curve.

Marko Jercic, Ivan Jercic, Nikola Poljak

The properties of decays that take place during jet formation cannot be easily deduced from the final distribution of particles in a detector. In this work, we first simulate a system of particles with well defined masses, decay channels, and decay probabilities. This presents the "true system" for which we want to reproduce the decay probability distributions. Assuming we only have the data that this system produces in the detector, we decided to employ an iterative method which uses a neural network as a classifier between events produced in the detector by the "true system" and some arbitrary "test system". In the end, we compare the distributions obtained with the iterative method to the "true" distributions.

Pablo García-Risueño

In the simulation of biological molecules, it is customary to impose constraints on the fastest degrees of freedom to increase the time step. The evaluation of the involved constraint forces must be performed in an efficient manner, for otherwise it would be a bottleneck in the calculations; for this reason, linearly-scaling calculation methods have become widely used. If integrators of order higher than 2 (e.g. Gear predictor-corrector methods) are used to find the trajectories of atoms, the derivatives of the forces on atoms with respect to the time also need to be calculated, which includes the derivatives of constraint forces. In this letter we prove that such calculation can be analytically performed with linearly scaling numerical complexity (O(Nc), being Nc the number of constraints). This ensures the feasibility of constrained molecular dynamics calculations with high-order integrators.

Konrad Jałowiecki, Marek M. Rams, Bartłomiej Gardas

We demonstrate how to compute the low energy spectrum for small ($N\le 50$), but otherwise arbitrary, spin-glass instances using modern Graphics Processing Units or similar heterogeneous architecture. Our algorithm performs an exhaustive (i.e., brute-force) search of all possible configurations to select $S\ll 2^N$ lowest ones together with their corresponding energies. We mainly focus on the Ising model defined on an arbitrary graph. An open-source implementation based on CUDA Fortran and a suitable Python wrapper are provided. As opposed to heuristic approaches, ours is exact and thus can serve as a references point to benchmark other algorithms and hardware, including quantum and digital annealers. Our implementation offers unprecedented speed and efficiency already visible on commodity hardware. At the same time, it can be easily launched on professional, high-end graphics cards virtually at no extra effort. As a practical application, we employ it to demonstrate that the recent Matrix Product State based algorithm-despite its one-dimensional nature-can still accurately approximate the low energy spectrum of fully connected graphs of size $N$ approaching $50$.

Nickolay Y. Gnedin

I describe a modification to the original Fast Multipole Method (FMM) of Greengard & Rokhlin that approximates the gravitation field of an FMM cell as a small uniform grid (a "gridlet") of effective masses. The effective masses on a gridlet are set from the requirement that the multipole moments of the FMM cells are reproduced exactly, hence preserving the accuracy of the gravitational field representation. The calculation of the gravitational field from a multipole expansion can then be computed for all multipole orders simultaneously, with a single Fast Fourier Transform, significantly reducing the computational cost at a given value of the required accuracy. The described approach belongs to the class of "kernel independent" variants of the FMM method and works with any Green function.

P. Bouton, P. V. Harris, W. Shorthose

H. Marschner, V. Römheld

Jin Cai, Yuee Xie, Po-Yao Chang et al.

Coexistence of topological elements in a topological metal/semimetal (TM) has gradually attracted attentions. However, the non-topological factors always mess up the Fermi surface and cover interesting topological properties. Here, we find that Ba3Si4 is a "clean" TM in which coexists nodal-chain network, intersecting nodal rings (INRs) and triple points, in the absence of spin-orbit coupling (SOC). Moreover, the nodal rings in the topological phase exhibit diverse types: from type-I, type-II to type-III rings according to band dispersions. All the topological elements are generated by crossings of three energy bands, and thus they are correlated rather than mutual independence. When some structural symmetries are eliminated by an external strain, the topological phase evolves into another phase including Hopf link, one-dimensional nodal chain and new INRs.

Victor Laliena, Javier Campo

A new discretization of the radial equations that appear in the solution of separable second order partial differential equations with some rotational symmetry (as the Schrodinger equation in a central potential) is presented. It cures a pathology, related to the singular behaviour of the radial function at the origin, that suffers in some cases the discretization of the second derivative with respect to the radial coordinate. This pathology causes an enormous slowing down of the convergence to the continuum limit when the two point boundary value problem posed by the radial equation is solved as a discrete matrix eigenvalue problem. The proposed discretization is a simple solution to that problem. Some illustrative examples are discussed.

Karl Werdan, Hans W. Heldt, Mirjana Milovancev

C. Aickin, R. Thomas

Andrea Muolo, Edit Mátyus, Markus Reiher

This paper presents the multi-channel generalization of the center-of-mass kinetic energy elimination approach [Mol. Phys., 111 2086 (2013)] when the Schrödinger equation is solved variationally with explicitly correlated Gaussian functions. The approach has immediate relevance in many-particle systems which are handled without the Born--Oppenheimer approximation and can be employed also for Dirac-type Hamiltonians. The practical realization and numerical properties of solving the Schrödinger equation in laboratory-frame Cartesian coordinates are demonstrated for the ground rovibronic state of the H$_2^+=\lbrace\text{p}^+,\text{p}^+,\text{e}^+\rbrace$ ion and the H$_2=\lbrace\text{p}^+,\text{p}^+,\text{e}^+,\text{e}^+\rbrace$ molecule.

Navdeep Rana, Pushpita Ghosh, Prasad Perlekar

We study spreading of a non-motile bacteria colony on a hard agar plate by using agent-based and continuum models. We show that the spreading dynamics depends on the initial nutrient concentration, the motility and the inherent demographic noise. Population fluctuations are inherent in an agent based model whereas, for the continuum model we model them by using a stochastic Langevin equation. We show that the intrinsic population fluctuations coupled with non-linear diffusivity lead to a transition from Diffusion Limited Aggregation (DLA) type morphology to an Eden-like morphology on decreasing the initial nutrient concentration.

T. Arnett, D. Dempster

R. Victor, L. Bertocci, S. L. Pryor et al.

Dongjun Wang, T. Imae

J. Parrish, J. Susko-Parrish, N. First