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April 2002

The Laboratory
in the News

Commentary by
William Goldstein

Quantum Simulations Tell
the Atomic-Level Story

Forensic Science Center Maximizes the Tiniest Clue

Bright Future for Compact Tactical Laser Weapons

Engineering's Tradition Turns Ideas into Reality

Patents

Awards

 

William Goldstein
Associate Director of Physics and Advanced Technologies

Physics Changes Focus


THE preeminent goal of physics in the 20th century was to understand the workings of the world at the most fundamental level. This moving target shifted to ever-smaller scales as the technology of observation—driven in turn by advances in physics—became more and more powerful.
As physicists studied atoms and their constituents, they learned that Newton’s laws of motion did not apply. For example, the particles that make up water molecules evidently do not follow the same set of rules as bulk samples of water. Convinced, however, that the world becomes more understandable as its basic constituents and interactions are exposed, physicists rarely considered systems of more than two interacting particles, unless they skipped directly to infinity. This reductive approach led to the triumphs of modern physics, including quantum mechanics and the standard model of the strong nuclear, weak nuclear, and electromagnetic interactions. To this day, however, many bulk properties of water remain a mystery.
As we enter a new century, geometric growth in computing power—also engendered by modern physics—has positioned physicists to address anew the complexities of many particles interacting to produce the bulk properties of materials. Using Advanced Simulation and Computing (ASCI) supercomputers to simulate the quantum mechanics of matter being shocked, researchers can now see in detail the dynamic activity of the atoms and molecules in the sample.
The article beginning on p. 4 describes the first-ever quantum molecular dynamics simulations of shocked hydrogen. Those simulations, the largest ab initio simulations ever done on the ASCI White computers, sought to find physical reasons for differing results from two sets of high-pressure experiments on deuterium, an isotope of hydrogen. Other simulations have examined the mechanical properties of water molecules under ambient conditions and at extreme pressures. For stewardship of the nation’s nuclear stockpile as well as for other programmatic applications, knowledge of how materials shock and fracture at the molecular level is essential.
An especially exciting area for quantum simulations is in the growing field of nanoscience. Nanomaterials—one nanometer is a billionth of a meter, or 100,000 times smaller than the width of a human hair—are the ultimate challenge to the way physicists count: one, two, . . . infinity. Ranging from around 10 to 1,000 atoms in size, nanoparticles behave in a complex way that is different from the behavior of both their atomic constituents and bulk matter. For the silicon nanoparticles known as quantum dots, quantum simulations reveal unique optical properties that vary with size and surface characteristics. Not only will lasers made of silicon be possible for the first time, but silicon dots may also be useful as fluorescent markers in biological research and as biological sensors. Quantum simulations are also exploring the behavior of DNA and how best to exploit a cancer-fighting drug.
As a tool for biological research, quantum simulation may engender progress akin to the advances in structural biology that followed the introduction of another physics tool, x-ray diffraction using synchrotron light sources. In fact, quantum simulations will play a key role in advancing biological imaging using fourth-generation light sources to illuminate proteins with the world’s most brilliant x-ray pulses. But that’s another story.




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UCRL-52000-02-4 | May 6, 2002