Ex nihilo crystal structure discovery

发现物质是由原子组成的是人类最伟大的成就之一。21世纪的科学主要是追求在原子水平上掌握（控制和理解）我们的环境。在生物学中，理解生命（保存生命，甚至试图创造生命）围绕着大而复杂的分子——RNA、DNA和蛋白质。全球变暖是由原子形成小温室气体分子（二氧化碳等）的特殊排列方式决定的。对更快、更高效、更便宜的计算机芯片的追求迫使纳米技术出现在我们面前。由于构成微观电路的晶体管越来越紧密，电子工程师必须了解原子在半导体和绝缘材料中的位置或错位。目前，天文学家每天都在发现太阳系外围绕外星恒星运行的新行星。最大的行星最容易被发现，而且许多比木星大得多。行星质量越大，构成其主体的物质所承受的压力就越大。在这种条件下，我们怎么能确定物质的结构呢？物质的原子理论导致了量子力学——一种微观的力学。原则上，要理解和预测物质在原子尺度上的行为，只需要求解量子力学薛定谔方程。这本身就是一个挑战，但现在以一种近似的方式快速计算相当大的原子集合的能量和性质是可能的。但是，仅凭我们对物理学的理解，是否有可能预测这些原子在自然界中的排列方式——从无到有？有些人认为物理科学连简单晶体的结构都不能常规地预测，这是一个丑闻，但大多数人认为这是一个非常困难的问题。必须在所有可能结构的多维空间中找到最小能量。那些有足够勇气应对这一挑战的研究人员是通过寻求复杂的算法来实现这一目标的——比如遗传算法，它呼吁进化来培育出更好的结构（更好的结构意味着更稳定）。然而，令我和其他人惊讶的是，我发现最简单的算法——把原子的集合扔进一个盒子里，然后在能量版图上往下移——如果重复多次，效果会非常好。这种方法不需要事先具备化学知识。事实上，科学家是通过结果来学习化学的——如果要用这种方法来预测物质在极端条件下的行为，这一点至关重要，因为在极端条件下，习得的直觉通常会失败。我已经使用了这种方法，我称之为随机结构搜索来预测晶体的结构。我的第一个应用是高压下的硅烷，我预测的结构最近已经在实验中出现了。但到目前为止，最令人印象深刻的应用可能是预测了在气态巨行星中发现的巨大压力下氢的结构，在那里它可能是室温超导体。在我的奖学金期间，我将扩展这项工作，尝试预测新发现的系外行星的物质结构，尝试发现和设计具有极端（希望是非常有用的）特性的材料，并帮助制药研究人员了解他们的药物分子在结晶时采用的多种形式。

The discovery that matter is made up of atoms ranks as one ofmankind's greatest achievements. Twenty first century science isdominated by a quest for the mastery (both in terms of control andunderstanding) of our environment at the atomic level.In biology, understanding life (preserving it, or even attempting tocreate it) revolves around large, complex, molecules -- RNA, DNA, andproteins.Global warming is dictated by the particular way atoms are arrangedto make small greenhouse gas molecules, carbon dioxide and so on.The drive for faster, more efficient, cheaper computer chips forcesnanotechnology upon us. As the transistors that make up themicroscopic circuits are packed ever closer together, electronicengineers must understand where the atoms are placed, or misplaced, inthe semiconducting and insulating materials.Astronomers are currently, daily, discovering new planets outside oursolar system, orbiting alien stars. The largest are the easiest tospot, and many are far larger than Jupiter. The more massive theplanet the higher pressures endured by the matter that makes up itsbulk. How can we hope to determine the structure of matter at theseconditions?The atomic theory of matter leads to quantum mechanics -- a mechanicsof the every small. In principle, to understand and predict thebehaviour of matter at the atomic scale simply requires the solutionof the quantum mechanical Schroedinger equations. This is a challengein itself, but in an approximate way it is now possible to quicklycompute the energies and properties of fairly large collections ofatoms. But is it possible to predict how those atoms will be arrangedin Nature - ex nihilo, from nothing but our understanding ofphysics?Some have referred to it as a scandal that the physical sciencescannot routinely predict the structure of even simple crystals -- butmost have assumed it to be a very difficult problem. A minimum energymust be found in a many dimensional space of all the possiblestructures. Those researchers brave enough to tackle this challengehave done so by reaching for complex algorithms -- such as geneticalgorithms, which appeal to evolution to breed ever betterstructures (with better taken to mean more stable). However, Ihave discovered to my surprise, and to others', that the very simplestalgorithm -- throw the collection of atoms into a box, and move theatoms downhill on the energy landscape -- is remarkably effectiveif it is repeated many times.This approach needs no prior knowledge of chemistry. Indeed thescientist is taught chemistry by its results -- this is critical ifthe method is to be used to predict the behaviour of matter underextreme conditions, where learned intuition will typically fail.I have used this approach, which I call random structure searching to predict the structure of crystals ex nihilo. My firstapplication of it has been to silane at very high pressures, and thestructure I predicted has recently been seen in experiments. Butprobably the most impressive application so far has been to predictingthe structure of hydrogen at the huge pressures found in the gas giantplanets, where it may be a room temperature superconductor.In the course of my fellowship I will extend this work to try toanticipate the structure of matter in the newly discovered exoplanets,to try to discover and design materials with extreme (and hopefully,extremely useful) properties, and to help pharmaceutical researchersunderstand the many forms that their drug molecules adopt when theycrystallise.