NIST’s James Sims and IU’s Stanley Hagstrom have calculated four excitation energies for the lithium atom approximately 100 times more accurately than any previous calculations or experimental measurements.
Precise determination of excitation energy—the amount necessary to raise an atom from a base energy level to the next higher—has intrinsic value for fundamental research into atomic behavior, but the success of the method the team employed has implications that go beyond lithium alone.
The theorists have overcome major computational and conceptual hurdles that for decades have prevented scientists from using quantum mechanics to predict electron excitation energies from first principles. Sims first proposed in the late 1960s that such a quantum approach could be possible, but its application to anything more than two electrons required a fiendishly difficult set of calculations that, until recently, was beyond the capacity of even the world’s fastest computers. In 2006 the team used a novel combination of algorithms, extended precision computing and the increase in power brought about by parallel computing to calculate the most accurate values ever for a simple, two-electron hydrogen molecule.**
By making improvements to those algorithms, Sims and Hagstrom now have been able to apply their approach to the significantly more difficult problem of lithium, which has three electrons. Much of the original difficulty with their method stems from the fact that in atoms with more than one electron the mutually repulsive forces among these tiny elementary particles introduces complications that make calculations extremely time-consuming, if not practically impossible.
Sims says that while the lithium calculation is valuable in itself, the deeper import of refining their method is that it should enable the calculation of excitation energies for beryllium, which has four electrons. In turn, this next achievement should enable theorists to predict with greater accuracy values for all of the remaining elements in the second row of the periodic table, from beryllium to neon, and potentially the rest of the periodic table as well. “The mathematical troubles we have with multiple electrons can all be reduced to problems with four electrons,” says Sims, a quantum chemist in the mathematics and computational sciences division. “Once we’ve tackled that, the mathematics for other elements is not any more difficult inherently—there’s just more number-crunching involved.”
To obtain their results, the researchers used 32 parallel processors in a NIST computer cluster, where they are currently working on the calculations for beryllium.
High precision determinations of excitation energies are of interest to scientists and engineers who characterize and model all types of gaseous systems, including plasmas and planetary atmospheres. Other application areas include astrophysics and health physics.
* J.S. Sims and S.A. Hagstrom. Hylleraas-configuration-interaction study of the 2 2S ground state of neutral lithium and the first five excited 2S states. Physical Review A, Nov. 19 2009, 10.1103/PhysRevA.80.052507.
** See “Algorithm Advance Produces Quantum Calculation Record,” NIST Tech Beat, March 16, 2006.
Chad Boutin | Newswise Science News
The balancing act: An enzyme that links endocytosis to membrane recycling
07.12.2016 | National Centre for Biological Sciences
Transforming plant cells from generalists to specialists
07.12.2016 | Duke University
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
07.12.2016 | Health and Medicine
07.12.2016 | Life Sciences
07.12.2016 | Health and Medicine