First-principles thermodynamics of metals under extreme conditions

作为一名宇航员的危险之一是，你的航天器可能会被以每小时数千英里的速度飞驰穿过太阳系的微小岩石颗粒和其他空间碎片击中。碰撞可能是可怕的，因为航天器的金属物体会以奇怪的方式工作，因为它被碰撞的力量加热和压缩。事实上，在许多其他情况下，真正的暴力事件会产生极端的影响。例如，想象一下，一枚导弹击中一艘战舰，一枚炸弹在有限的空间内爆炸，或者一颗大型陨石击中地球。为了了解这些情况，科学家们想知道金属和其他类型的材料在受到比大气压力大数百万倍的巨大压力时，以及当它们被加热到数千摄氏度时的表现。我们项目的想法是使用计算机计算来计算出金属在非常高的压力和温度下的表现。要了解我们计划如何做到这一点，你必须记住，一切都是由原子组成的，一种材料与另一种材料的不同之处在于，它是由不同的原子以不同的方式排列而成的。为了弄清楚金属在受到强烈压缩和加热时的行为，我们将对原子集合进行计算，看看当原子被挤压在一起时会发生什么，当它们被给予大量热能时会发生什么。我们将使用量子力学理论来实现这一点，该理论准确地告诉我们如何计算原子的行为。我们知道这样的计算真的很有效，因为我们已经在铝和铜等一些金属上进行了尝试，我们发现这些计算非常准确地告诉我们，金属必须达到多热才能熔化。你可能会奇怪我们为什么要做计算。为什么不直接做实验室实验呢？多年来，科学家们一直在这样做。一种被称为静态压缩的方法是用大钳子非常用力地挤压材料。另一种称为冲击实验的方法是向材料发射高速子弹--就像岩石颗粒击中航天器一样！这两种实验都可以达到数百万倍的大气压和数千度的温度。但问题是实验很困难，有时冲击实验和静态压缩实验不太吻合。因此，我们需要计算来帮助理解实验，并解释为什么它们不一致。计算如此重要还有另一个很好的原因。实验很擅长告诉你发生了什么，但它们可能不会告诉你为什么会发生。为了理解为什么一种材料以一种方式而不是另一种方式表现，你必须进行计算。只有对原子的计算才能真正让你更好地理解。在我们的项目中，我们想要看看一种名为过渡金属的金属家族，其中包括一些众所周知的金属，如铁、镍和钨，以及一些不太知名的金属，如Hf和Mo。这是一个很好的计划，因为家庭关系将帮助我们建立一个令人信服的故事，说明它们在高压和高温下的行为是如何从一种金属变化到另一种金属的。当我们完成这个项目时，许多其他科学家会对我们的发现感兴趣。我们将比以前更好地了解金属在高压和高温下会发生什么，以及如何用原子的行为来解释这一点。做实验的科学家将有助于理解为什么不同的实验有时会不一致。从长远来看，我们的工作将帮助太空科学家设计更好的航天器，并减少宇航员的生命危险！

One of the hazards of being an astronaut is that your spacecraft could be hit by small rock particles and other space debris hurtling through the solar system at thousands of miles an hour. The collisions could be terrifying, because the metal body of the spacecraft would behave in strange ways as it is heated and compressed by the force of the collisions. Actually, there are many other situations where really violent events have extreme effects. Imagine, for example, a missile hitting a battleship, a bomb exploding in a confined space, or a large meteorite hitting the Earth. To understand these situations, scientists would like to know how metals, and other kinds of materials, behave when they are squeezed by enormous pressures millions of times greater than atmospheric pressure, and when they are heated to temperatures of thousands of degrees.The idea in our project is to use computer calculations to work out how metals behave at very high pressures and temperatures. To understand how we are planning to do this, you have to remember that everything is made of atoms, and what makes one material different from another is that it is made of different atoms arranged in different ways. To work out how metals behave when they are strongly compressed and heated, we are going to do calculations on collections of atoms to see what happens when the atoms are squeezed together and when they are given a lot of heat energy. We will do this using the theory of quantum mechanics, which tells us exactly how to calculate the behaviour of atoms. We know that calculations like this really work, because we have tried them already on some metals like aluminium and copper, and we have found that the calculations tell us very accurately how hot the metals have to be in order to melt.You might wonder why we want to do calculations. Why not just do laboratory experiments? Scientists have been doing just that for many years. One way, called static compression , is to squeeze the material very hard using a large vice. Another way, called shock experiments , is to fire high-speed bullets at the materials -just like rock particles hitting spacecraft! Both kinds of experiments can reach pressures of millions of times atmospheric pressure and temperatures of thousands of degrees. But the problem is that the experiments are difficult, and sometimes shock experiments and static compression experiments do not agree with each other very well. So we need calculations to help understand the experiments and to explain why they don't agree.There is also another good reason why calculations are so important. Experiments are very good at telling you what happens, but they may not tell you why it happens. To understand why a material behaves one way rather than another, you have to do calculations. And it's only calculations on the atoms that can give you a really good understanding.In our project, we want to look at a family of metals called the transition metals , which include some well-known metals like iron, nickel and tungsten, as well as some less well-known ones like hafnium and molybdenum. This is a good plan, because the family relationships will help us to build a convincing story about how their behaviour at high pressures and temperatures changes from one metal to the next.When we have finished the project, many other scientists will be interested in what we have discovered. We will understand much better than before what happens to metals at high pressures and temperatures, and how this is explained by the behaviour of the atoms. Scientists doing experiments will be helped to understand why different experiments sometimes do not agree. And in the long term our work will help space scientists to design better spacecraft, and make the astronaut's life less hazardous!