实验十附件-晶体结构分析虚拟仿真实验参考文献实验讲义

JULY 31,1913NATURE55effect that such a device increasesthe number ofThe Structure of the Diamond.degrees of freedom of the apparatuswith an accom-Wg have applied the new methods of investigationpanying increase in the number of possible oscilla-involving the use of X-rays to the case of the diamond,tions and of conditions necessary for stability is,and have arrived at a result which seems of consider-believe,incontrovertible.Oneform of dynamicalable interest.The structure is extremely simple.instability that may result in such cases is the settingEvery carbon atom has four neighbours at equal dis-up of violent oscillations,ever increasing in ampli-tances from it,and in directions symmetrically relatedtude,in the pendulum itself,accompanied by flappingto each other.The directions are perpendicular toof the control planes,in which'case this particularthe four cleavage or (planes of the diamond;method of control becomes worse than useless.parallel,therefore,to the four lines which join theThe remedy which naturally suggests itself,in suchcentre of a given regular tetrahedron to the fourcircumstances,is to damp down the oscillations of thecorners.The elements of the whole structure are fourpendulum by means of frictional or other resistances,directions and one length,the latter being,in fact,and it is probable that few university graduates who152 x Io-s cm.There is no acute angle in the figure.have taken first-class honours in mathematics wouldThese facts supply enough information for the con-think that such a contrivance could possibly be wrong.struction of a model which is easier to understandThe following test case will show how very dangerousthan a written description.it is to attempt to draw conclusions from generalIf we proceed from any atom,using only standardconsiderations.directions,to the next but one,the straight line join-For the acroplane or torpedo,we substitute a heavying the first to the last is a diagonal of a face of therigid body POR,free to rotate without resistancecubical element of structure;if we move in the sameabout a horizontal axis through its centre of gravityway through four stages,using all four standardO,perpendicular to the plane of the paper,and there-directions in turn,the straight line joining the firstfore,in the absence of othercauses,in neutraland the last is a cube edge.Starting fromany atomequilibrium,and we assume that themomentofwe can return to it after six stages,using threeinertia of this body is considerable.standard directions twice each.In this way weWe next imagine a light,small pendulum OOtoalways link together rings of six carbon atoms.be fixed in bearings in the body POR,so that it canIf the structure is looked at along a cleavage planeturn about the same axis,but we suppose thatit is seen that the atoms are arranged in parallelfrictional couple iscalledplanes containing equal numbers of atoms,butRinto playbetween the largeseparated by distances which alternate and are in thebody and the pendulum at