(Diamond Foundry) Diamond Foundry says it grows its diamonds layer-by-layer from a superheated plasma. Diamonds are a girl's best friend, but they don't grow on trees. Or do they? The Santa Clara-based startup Diamond Foundry claims it can grow diamonds in a lab that are as high-quality as natural gems, minus the exploitation of the mining industry. Actor Leonardo DiCaprio, along with 10 billionaires, have already invested in the company, which says it can make hundreds of diamonds in two weeks, weighing up to nine carats each. But how exactly are these diamonds made, and how does it differ from existing synthetic methods? The company's website is short on details, but here's what we know: They start with a real diamond as a seed crystal. (This is what make their product different from other synthetic diamonds, according to a company spokesperson.) Then, using a super heated plasma, they build more atoms onto this seed, layer by layer, until they have a diamond. The gems are grown in chemical reactors that can reach a scorching 8,000 degrees Celsius (more than 14,000 degrees Fahreneit) — hotter than the surface of the sun , which is about 5,500 degrees Celsius. We chatted briefly with Catherine McManus, chief scientist of Materialytics , a company that specializes in distinguishing natural, synthetic, and fake diamonds, to find out what separates Diamond Foundry's gems from other synthetic diamonds. (Diamond Foundry) Diamonds created by Diamond Foundry. How to make a diamond Diamonds are made of carbon, the same material found in pencil graphite. In nature, geologists believe diamonds are created over millions of years under intense pressure and temperature in the Earth's mantle, and then regurgitated onto the surface by volcanoes. By contrast, synthetic diamonds are made in a lab. Chemically, natural and synthetic diamonds are almost identical, but they can vary in the trace elements found inside. The two most common techniques for making synthetic diamonds are known as high-pressure high-temperature (HPHT) and chemical vapor deposition (CVD). In HPHT , a carbon seed crystal is placed inside a device called a press with a metal solvent and subjected to immense pressures at temperatures around 1,400 degrees Celsius (about 2,250 degrees Fahrenheit), which melts the metal. The molten metal dissolves the carbon crystal, and it solidifies into a diamond. In CVD , a carbon-hydrogen gas mixture is deposited on a surface layer-by-layer. This process usually takes place at about 800 degrees Celsius (1,470 degrees Fahrenheit). Diamond Foundry's method seems to be a combination of HPHT and CVD, said McManus. It's basically the latter method, but at much higher temperatures, she said. The result are diamonds that are as pure as natural ones, the company claims, But ethically and morally pure as well. 下面的是另外一篇报道： Diamonds are a girl’s best friend, but they don’t grow on trees. Or do they? The Santa Clara-based startup Diamond Foundry claims it can grow diamonds in a lab that are as high-quality as natural gems, minus the exploitation of the mining industry. Actor Leonardo DiCaprio, along with 10 billionaires, have already invested in the company, which says it can make hundreds of diamonds in two weeks, weighing up to nine carats each. But how exactly are these diamonds made, and how does it differ from existing synthetic methods? The company’s website is short on details, but here’s what we know: They start with a real diamond as a seed crystal. (This is what make their product different from other synthetic diamonds, according to a company spokesperson.) Then, using a super heated plasma, they build more atoms onto this seed, layer by layer, until they have a diamond. The gems are grown in chemical reactors that can reach a scorching 8,000 degrees Celsius (more than 14,000 degrees Fahreneit) — hotter than the surface of the sun , which is about 5,500 degrees Celsius. We chatted briefly with Catherine McManus, chief scientist of Materialytics , a company that specializes in distinguishing natural, synthetic, and fake diamonds, to find out what separates Diamond Foundry’s gems from other synthetic diamonds. Diamonds are made of carbon, the same material found in pencil graphite. In nature, geologists believe diamonds are created over millions of years under intense pressure and temperature in the Earth’s mantle, and then regurgitated onto the surface by volcanoes.
Being happy is a choice by June I have chosen to be happy, even after having shed some (sad) tears from time to time. Most of my friends see only the sunny side of me; a very few saw the cloudy me. You were always like sunshine, butnow I know your heart can be heavy, too. This year, I tried to write some personal greetings to friends and loved ones before Christmas, but eventually I surrendered to e-cards of mass mailing. This gives me a chance to “reply” with more personal touch. A few students and clients remembered me by sending me greetings, for which I am grateful. A few friends sent me year-endletter, to whom I responded with my own version of the letter. All these communications make me busy and happy, but only one email touched my soul. In a moment like this, I believe there must be a life before present, and a life after this. You and I must have be lovers 500 years ago, as a Buddhist wouldsay. How else could we meet during a spring break in the paradise by chance, and became soul mates? It is such a wonderful feeling when two strangers in this big world would become close friends. I do hope to meet you again, someday, in this life. Merry Christmas to you…
关注： 1） ELF的定义； 2） 计算原理及流程。 题记：赠人玫瑰，手留余香。 相逢是一种缘。旅途中，有一种人，当你不经意间想起，总是满怀感激......XinXin Zhang 和 Meiguang Zhang即属于这种人。 新问题：正确设置INCAR，VASP533版本千万不要加IBRION=2，否则会陷入死循环 EXEC=/db/home/yexq/software/vasp533/vasp.5.4.1/vasp.5.4.1/bin/vasp_std 可快速成功计算ELF的VASP版本 一般设置0.5 为起点 isosurface value of 0.5 and 0.7, SYSTEM=Static- self-consistent PREC = Accurate ENCUT = 600 EDIFF = 1e-6 ISTART = 0; IBRION = 2 POTIM = 0.1 ISMEAR =1; SIGMA = 0.2 LELF=T 正确的INCAR设置-from Shichang Li SYSTEM=Static- self-consistent PREC = Accurate ENCUT = 400 EDIFF = 1e-6 ISTART = 0 POTIM = 0.1 ISMEAR =1; SIGMA = 0.2 KSPACING=0.2 KGAMMA=.TRUE. LELF=.TRUE. 关于IBRION参数 Default: IBRION= -1 for NSW=0 or NSW=1 = 0 else IBRION=2 A conjugate-gradient algorithm (a simple discussion of this algorithm can be found for instance in ) is used to relax the ions into their instantaneous groundstate 关于KSPACING参数 KSPACING -tag and KGAMMA -tag KSPACING = KGAMMA = Default: KSPACING = 0.5 KGAMMA = .TRUE. The tag KSPACING determines the number of k-points if the KPOINTS file is not present (see Sec. 5.5 ). KSPACING is the smallest allowed spacing between k-points in units of Å . The number of k-points increases when the spacing is decreased. The number of k-points in the direction of the first, second and third reciprocal lattice vector is determined by the equations These values are rounded to the next integer. The generated grid is either centred at the point (e.g. includes the point) ( KGAMMA =.TRUE.) or is shifted away from the point, as usually done for Monkhorst Pack grids ( KGAMMA =.FALSE.) (compare Sec. 5.5.3 ). Per default, the grids include the point. 哪一种方法设置的K点更密：KSPACING or KPOINTS？ 可通过查看IBZKPT中k点个数，来看哪一种更密 The three qualities of k-point separation for CASTEP (1/Angstrom) coarse.le..08 medium.le..05 fine.le..04 Please input the quality of Monkhorst-Pack grid (Default is .035) 0.03 Reciprocal lattice parameters 0.84446874 2.56760472 2.41391726 Mesh parameters of Monkhorst-Pack grid 1. “Electronlocalization function” ，电子局域化函数。用来描述以某个位置处的电子为参考，在其附近找到与他同自旋的电子的概率，可以表征这个作为参考的电子的局域化程度，也是一种描述在多电子体系中的电子对概率的方法。 2. 一些公式： :电子局域化函数 0 ≤ ELF ≤1 , ELF=1 对应完全局域化，ELF=1/2，对应类电子气型的成对概率。 ：均匀电子气的，自旋密度等于 (r)的局域值 ：反映电子局域化的信息 ：在r位置，s半径内找到两个同自旋的电子的几率，做Taylor 展开，中括号中的项就是上边的D , 这个值越小，说明在上述区域找到相同自旋的电子的几率越小，那么这个电子的局域性越高。 3. 这个函数是由 AxelD. Becke 和 K. E.Edgecombe 在 1990 年定义的 . 详 细的定义和公式请看参考文献和下面给出的链接。 这个函数能很有效的分析电子局域化程度，比如分析重元素的电子壳层排布结构，在分子中，通过 ELF 可以清晰的分出核态和价态，也能显示出共价键和未共用的电子对。这在我们分析成键中可能会有很大的帮助。 二． 计算和画图 1. vasp 进行自恰计算 使用一般自恰计算的四个输入文件，在 INCAR 中一定要加入开关 LELF=T, 其他设置不变。例如： SYSTEM=Static- self-consistent PREC = Accurate ENCUT =800 EDIFF = 1e-6 ISTART = 0; IBRION = 2 POTIM = 0.1 ISMEAR =1; SIGMA = 0.2 LELF=T 这样是为了让包含 “ 电子局域密度函数 ” 信息的 ELFCAR 文件保存下来。这个文件的格式和 CHGCAR 文件的类似，详细可以参见 vasp 手册，这里不做介绍。 2. 绘图的时候可以使用 xcrysden 和 vaspview 两种软件。 在使用 xcrysden 查看 ELFCAR 文件的时候需要先要将这个文件用 v2xsf 程序将其转化为 *.xsf 格式的 xcrysden 可读文件。 xcrysden 软件的使用大家一般比较熟悉，它可以画 xy, xz, yz 二维平面图，也可以画三维空间图 。 Vaspview 同样可以画二维和三维两种图。 一个专门的 ELF 介绍网站 ： http://www.cpfs.mpg.de/ELF/index.php?content=01quant/01def.txt 附-网言摘录 希望大家先帮看看我的计算流程原则上是不是正确的，然后说说计算精度的问题。 我的计算流程： geo-opt----scf----elf and bader scf 后, mkdir elf bader cp scf/* elf/. INCAR做如下修改： ICHARG =11 #MAGMOM = * * * LELF = T LWAVE = F 其它不变。k-mesh不变 cp scf/* bader/. INCAR做如下修改： ICHARG = 1 #MAGMOM=* * * LAECHG = T LWAVE = F 其他不变。k-mesh不变。 以上两个性质计算中，elf是做非自洽计算的，我的理解是，elf仅仅作为初始电荷密度的数值处理，不需要做自洽计算。而bader需要原子价层电子和内层电子，一般vasp的PAW方法不提供内层电子，所以需要以上一步scf电荷密度做输入，来补全电荷密度。原则上这两个任务设置有问题没？ 精度方面，elf计算为了提高精度（图的饱满平滑），需要调高NGX(Y,Z)，然后重新做静态自洽计算。这个不必提高k采样密度，保持不变就好。 bader计算说要适当调高NGX(Y,Z)，使得总电子数等于实际电子数。这个总电子数是不是为bader分析结果文件ACF.dat的最后一行给出的电荷数？ 附-from 上述网站的介绍 Original definition of ELF The electron localization function (ELF) was introduced by Becke and Edgecombe as a simple measure of electron localization in atomic and molecular systems . The original formula is based on the Taylor expansion of the spherically averaged conditional same-spin pair probability density to find an electron close to a same-spin reference electron. The main aspect of this formulation is that thus defined ELF is a property of the same-spin pair density . The same-spin pair probability density P 2 ( r , r' ) is the probability density to simulaneously find two like-spin electrons at positions r and r' . In Hartree-Fock (HF) approximation: P 2 ( r , r' ) = rho( r ) ρ( r' ) − |ρ 1 ( r , r' )|2 The conditional same-spin pair probability density P cond ( r , r' ) is the probability density to find an electron at some position r' if a like-spin reference electron is located with certainty at position r . In Hartree-Fock (HF) approximation: P cond ( r , r' ) = ρ( r' ) − |ρ 1 ( r , r' )|2 ⁄ ρ( r ) with the electron densities ρ( r ) and ρ( r' ), and the σ-spin one-particle density matrix ρ 1 ( r , r' ) of the HF determinant: ρ 1 ( r , r' ) = ∑ i σ ψ i * ( r' )ψ i ( r ) where the summation runs over all occupied σ-spin (i.e. either up or down spin) orbitals ψ i ( r ). The probability density to find a like-spin electron at a distance s from the reference point r can be found by a Taylor expansion of the spherically averaged conditional same-spin probability density P cond ( r , s ) (the spherical average is on a shell of radius s around the reference point r ). The first ( s independent) term of the Taylor expansion vanishes, because the conditional probability density to find two like-spin electrons at the same position r is, as a direct consequence of the Pauli principle, equal to zero. The linear term is dependent on the gradient of the HF Fermi hole at r - thus it vanishes as well. The leading (quadratical) term of the Taylor expansion of the spherically averaged conditional same-spin probability density is : P cond ( r , s ) = 1⁄3 s2 + ... The expression in the brackets is besides a ρ factor proportional to the Fermi hole mobility function of Luken and Culberson and is related to the curvature of the HF Fermi hole at r as shown by Dobson . Becke and Edgecombe associated the localization of an electron with the probability density to find a second like-spin electron near the reference point. The smaller this probability density, i.e. the smaller the expression D( r ) = ∑ i σ | ∇ψ i ( r ) | 2 − ¼ | ∇ρ( r ) | 2 ⁄ ρ( r ) of the quadratic term, the higher localized an electron is. Thus, the Pauli repulsion between two like-spin electrons, described by the smallness of D( r ), is taken as a measure of the electron localization. Using the corresponding factor found for uniform electron gas D h ( r ) Becke and Edgecombe defined ELF as follows: η( r ) = 1 ⁄ with χ BE ( r ) = D( r ) ⁄ D h ( r ) where D h ( r ) = 3/5 (6π2) 2/3 ρ( r ) 5/3 Given by the definition, ELF values are bound between 0 and 1. In the seminal paper of Becke and Edgecombe the ratio χ BE ( r ) was attributed to a dimensionless localization index calibrated with respect to the uniform electron gas as a reference. Nevertheless, it should be mentioned that this reference was chosen arbitrarily (originally, Luken and Culberson had defined a function similar to χ BE ( r ), but instead of a division they preferred a subtraction, again arbitrarily choosing the uniform electron gas as a reference). The only measure of the electron localization, as described by the two authors, is the expression D( r ). However, ELF cannot yield the value of D( r ) - i.e. the actual measure of the electron localization - because it depends, through D h ( r ), on the electron density as well. In this sense, ELF is a relative measure of the electron localization. High ELF values show that at the examined position the electrons are more localized than in a uniform electron gas of the same density. η( r ) = 1⁄2 indicates that the effect of the Pauli repulsion is the same as in the uniform electron gas of the same density. Of course, it cannot be compared with the uniform electron gas with respect to other properties (it is obvious that the electron density gradient in an atom, molecule or solid differs from zero almost everywhere). See also section How to interpret . ELF for density functionals In density functional theory the pair density is not explicitly defined. Thus, the original formulation of ELF derived from the pair density is not applicable. Searching for a possibility to use ELF in density functional calculations, Savin et al. utilized the observation that the Kohn-Sham orbital representation of the Pauli kinetic energy density has the same formal structure as the expression D( r ) of Becke and Edgecombe. The main aspect of Savin's formulation is that thus defined ELF is a property based on the diagonal elements of the one-particle density matrix, i.e. the electron density . In the Kohn-Sham method the kinetic energy of N noninteracting electrons is: T s = ½ ∫ ∑ i N | ∇ψ i ( r ) | 2 dv with the Kohn-Sham orbitals ψ i ( r ). The positive definite kinetic energy density t( r ) = ½ ∑ i N | ∇ψ i ( r ) | 2 is bounded by a minimum value: t( r ) ≥ 1⁄8 | ∇ρ( r ) | 2 ⁄ ρ( r ) when all orbitals are proportional to √ρ (i.e. like in a bosonic system) . The Pauli kinetic energy is the energy due to the redistribution of the electrons in accordance with the Pauli principle. It is the integral of the Pauli kinetic energy density: t P ( r ) = t( r ) − 1⁄8 | ∇ρ( r ) | 2 ⁄ ρ( r ) The Pauli kinetic energy density itself does not resolve the bonding situation. It is the more or less arbitrary division of t P ( r ) by the kinetic energy density of a uniform electron gas of the same electron density (with the Fermi constant c F = 3⁄10 (3π2) 2/3 ) t h ( r ) = c F ρ( r ) 5/3 that yields all the information. For a closed shell system the ratio χ S ( r ) = t P ( r ) ⁄ t h ( r ) is formally identical with the ratio χ BE ( r ) in the HF approximation. This identity holds also for an open shell system, when the kinetic energy densities are computed for the corresponding spin part only. Then also the ELF formulas based on χ BE ( r ) and χ S ( r ) respectively, are identical. In the interpretation of Savin et al. ELF is a measure of the influence of Pauli principle as given by the Pauli kinetic energy density, relative to a uniform electron gas of the same density. Similarly to the original definition, ELF does not mirror t P ( r ). An expression equivalent to χ S ( r ) of Savin et al. was found already 1983 by Deb and Ghosh . Deb and Ghosh were searching for a proper local description of the kinetic energy density. They proposed the following formulation of the kinetic energy density: t( r ) = −¼ ∇2ρ( r ) + 1⁄8 | ∇ρ( r ) | 2 ⁄ ρ( r ) + c F f( r ) ρ( r ) 5/3 The right hand side of the above equation consists, besides the density Laplacian that vanishes by an integration over the whole space, of the full Weizsäcker term 1⁄8 | ∇ρ( r ) | 2 ⁄ ρ( r ) and a modified Thomas-Fermi term with a correction factor f( r ). Substituting for the left hand side the Hartree-Fock expression for the kinetic energy density: t( r ) = ½ ∑ i | ∇ψ i ( r ) | 2 − ¼ ∇2ρ( r ) unveils the correction factor f( r ) of Deb and Ghosh as the ratio χ S ( r ) of Savin. Besides calculating f( r ) for noble gas atoms (revealing the atomic shell structure) Deb and Ghosh did not further exploit this function.
I don’t know, but I agree with what Ralph Waldo Emerson wrote in On Friendship in 1841:” In a friend, what I am looking for is not a mush of concessions, a person who would agree with everything that I say; rather what I’m looking for is a beautiful enemy, a person who will challenge me, who will push me, who will help me in my apprenticeship to the truth.” This is also what I do to my friends: challenge them, push them, as well as help them. So, I will not always say nice things to my true friends, but I can say nice things all the time to those I don’t care...I am lucky enough to have a few friends before whom I can say anything in my heart, without thinking about too much.
Your friend is your needs answered. He is your field which you sow with love and reap with thanksgiving. And he is your board and your fireside. For you come to him with your hunger, and you seek him for peace. When your friend speaks his mind you fear not the "nay" in your own mind, nor do you withhold the "ay." And when he is silent your heart ceases not to listen to his heart; For without words, in friendship, all thoughts, all desires, all expectations are born and shared, with joy that is unacclaimed. When you part from your friend, you grieve not; For that which you love most in him may be clearer in his absence, as the mountain to the climber is clearer from the plain. And let there be no purpose in friendship save the deepening of the spirit. For love that seeks aught but the disclosure of its own mystery is not love but a net cast forth: and only the unprofitable is caught. And let your best be for your friend. If he must know the ebb of your tide, let him know its flood also. For what is your friend that you should seek him with hours to kill? Seek him always with hours to live. For it is his to fill your need, but not your emptiness. And in the sweetness of friendship let there be laughter, and sharing of pleasures. For in the dew of little things the heart finds its morning and is refreshed.
标签: friend
