What is First Principle Calculation?

         After the establishment of quantum mechanics, and in accordance with the principle of statistical physics, the macroscopic properties of microscopic state are determined. The difference with classical physics is how to express microscopic state of the system? In classical physics can be simply expressed by position and momentum, but the presentation of framework in quantum mechanics is changed. Because in quantum mechanics, the position and momentum cannot both be accurately measured simultaneously.

How to do it?

Represent in wave functions. Square of the wave function represent the probability of particles appeared, this is statistical interpretation of wave function. Then, how to get the electron’s wave function? This is done by solving the Schrodinger equation.

         However, solving the Schrodinger equation is extremely difficult. Except for a few simple system i.e. Hydrogen atom, Schrodinger equation are difficult to obtain analytical solution. Thereafter, in order to apply the principles of quantum mechanics, Hartree and Fock proposed self-consistent field, which is SCF method. Here, field actually is a mean-field, that is, the potential field where particles in is replaced by a mean potential field, here included one electron approximation.

What is self-consistent field method?

This is no more science, whose interested can look at the Xie Xide band theory of solids. In general, those based on the Hartree-Fock self-consistent field is called first principle methods. This is the first source of the first principle methods, also called ab initio methods.

Why it is called ab initio methods?

Because this method which developed based on the principles of quantum mechanics requires only seven physical constants – the speed of light, Planck’s constant, atomic fine-structure constant, the electron mass, electron charge, nuclear mass, and nuclear charge, then we can calculate almost every properties of materials in ground state.Because not depend on the experiment, so is called ab initio methods.

         In addition, the source said it was from "the first impetus", the religious vocabulary. Newton founded the first impetus, because Newton's first law describes the substance remains stationary or in uniform motion without external force. If the universe was born at the beginning of all things should be static, but had later in the movement, how come it is moving? Newton believed that this is due to pushed of the God, and Newton later years committed to Theological Studies. Modern science believes that universe originated from the Big Bang, but the explosion also need a reason of it. All of these hard to explain things are attributed to "the first impetus" problem of universe.
         Science does not believe in God, we do not know "the first impetus" problem is merely because our scientific knowledge is imperfect. The first push certainly caused by some principle. This could be the "first principles." Einstein later years committed to "grand unified field theory" research, it is hoped to find "the first prinple" of all the physics laws, unfortunately, it was the level of science can not reach at that time. Now too far no answer.
(This paragraph is taken from: http: //baike.baidu.com/view/1278387.htm)

         Another first principle designation is derived from the Kohn-Sham method. Because the square of the wave function is equivalent to the probability of electron appear, then using probability density of electrons as a variable brought a great convenience. If wave functions as a variable, for N particle system, each particle described with a wave function, then would have 3N variables, since each particle has a xyz coordinates, three degrees of freedom, N particles have 3N variables, N is generally Avogadro constant magnitude. Difficult to solve! However, if the electron density is taken as the variable, just to be able to give electron density at any point, which is actually three variables, i.e., Rou (x, y, z), Rou is electron density.

Can electron density to be used as a variable?

Using a 3-dimensional variable to replace a 3N-dimensional variable will it lose information?

Hohenberg and Kohn proved two theorems, the density functional theory, the famous H-K theorem of first principle. Interested go to the website look how to prove.

Theorem along the following lines: a non-degenerate ground state wave function is the only function of the electron density; the second is, if the electron density is determined, then the unique nature of the ground state is determined. Since then, Kohn and Sham (沈吕九) develop this approach, called the density functional theory, Kohn received Nobel Prize in Chemistry for this work. Note: The physicist won the Nobel Prize in Chemistry, another is seemingly physicist Rutherford, the 20th century's greatest experimental physicist.

         In summary, the first principle is the title of ab initio methods based on density functional theory, or based on ab initio Hartree-Fock self-consistent field method.

taken from http://emuch.net/html/201106/3227802.html

physics story

          Long time ago, our great physicist Sir Isaac Newton founded classical mechanics, that is, the mechanical movements, energy, momentum that compile the foundation to university students of science.

         Classical mechanical point of view is absolute. In classical mechanics, one knowing the position and momentum of an object, the state of the object can be uniquely determined. In other words, the position and velocity of the object is predictable.

         He achieved great success in terms of macroscopic and low speed system, for example, an astrophysicist at once, by Newtonian mechanics, predicted trajectory of  Neptune, and then is found by an astronomer. This is an example of excellent application of classical mechanics.  (http://wenku.baidu.com/view/c4b3a465783e0912a2162a9e.html)

         Next, Ostered, Faraday, ... , discovered the electric-magnetic interactions. Great physicist Maxwell then governed almost all electromagnetic phenomena to a set of four equations. At this time the development of physics seem to be at summit.

         In fact, Kelvin, Gibbs, Helmholtz,... and the master of statistical physicist Boltzman, setting up the thermodynamics given the relation between macroscopic and microscopic state. Simply put, according to Newton’s classical laws of motion plus Electromagnetic theory, statistical averaging on the mechanism of microscopic atoms giving a nature system of almost like of macroscopic system, thanks to the famous Maxwell-Boltzmann statistical formulas.

         However, the blackbody radiation, hydrogen atom spectroscopy, photoelectric effect, Compton effect lead to quantum mechanics level. The salient features of quantum mechanics theory is non-absolute. In quantum mechanics, everything is relative, not absolute. The most apparent slogan is light is either wave or particle. After being extended by de Broglie, noting all matter has wave
Particle duality. Wave-particle duality led to many consequences, one of which is the famous Heisenberg uncertainty principle.
         For example, in quantum mechanics, the position and momentum of the particle can not  be measured accurately in simultaneous, and so for energy and time can not be measured accurately in simultaneous. That is, if the measured particle momentum is absolutely accurate, then the measured location of the particle necessary to galaxy-inaccurate. If you want to measure accurately energy of the particles, it would take an infinite amount of time, thanks to the wave-particle duality nature. After Planck, Heisenberg, de Broglie, Schrodinger, Bonn, Bohr, Pauli and others efforts, quantum mechanics Established.




noted! mostly content here is directly taken from http://emuch.net/html/201106/3227802.html

Quantum espresso -5.0.2 parallel exe -- some notes on parallel installation

if you got massage like

from test_input_xml: Empty input file

the reason may is your pw.x is installed to run in series not parallel.

to check whether your pw.x exe is series or parallel, one simple way is to check the xx.scf.out file, at the first few lines

-------------------------------------------------------------

solution:

step 1) install those libmpich.... like patch from your software centre, then restart

step 2) create the mpi lib path to etc/ld.so.conf.d

ie. http://www.cyberciti.biz/faq/linux-setting-changing-library-path/

for my case; I added user/lib/openmpi/lib; use/lib/openmpi/lib/openmpi

step 3) recompile the QE

       ./configure clean

       ./configure F90=gfortran (may trouble using ifort with mpi)

       ./make all

Comparison between HAMR and MAMR

3        Comparison between HAMR and MAMR

Both shared a similar characteristic, which is high effective writing field gradient can

achieved. The effective writing field gradient is no longer contribute from the magnetic character of the recording head but is determined by the external assisted energy.

            For HAMR to be in product state, the thermal issues, optical issues need to solve and the way to integrate the laser source to the recording head also need to determine.

            While for MAMR, in order to be in product state, more practical research on STO is required. The most disadvantage of MAMR is that the Ku(FGL) µ Hk²(media).

References

[1]   R. H. Victora, et al., “Areal Density Limits for Perpendicular Magnetic Recording,” IEEE Trans. Magn., Vol. 38, No. 5 2002.

[2]   H. N. Bertram and M. Williams, “SNR and Density Limit Estimates: A Compararison of Longitudinal and perpendicular Recording,” IEEE Trans. Magn., Vol. 36, No. 1 Jan 2000.

[3]   Roger Wood, “The Feasibility of Magnetic Recording at 1 Terabit per Square Inch,” IEEE Trans. Magn., Vol. 36, No. 1 Jan 2000.

[4]   W. A. Challener, et al., “The Rod to HAMR”, FB-2, APMRC 2009, Grand Hyatt Hotel, Singapore, Jan. 14-16, 2009.

[5]   S. M. Mansfield and G. S. Kino, “Solid immersion microscope”, Appl. Phys. Lett., vol. 57, pp. 2615-2616, 2005.

[6]   Mark H. Kryder, et al., “Heat Assisted Magnetic Recording”, Proceedings IEEE, vol. 96, No. 11, November 2008.

[7]   B. X. Xu, et al., “Thermal effects of heated magnetic disk on the slider in heat-assisted magnetic recording”, JAP 99, 2006.

[8]   B. X. Xu, et al., “Characterization of media cross-track thermal profile in heat-assisted magnetic recording”, JMMM 320, pp. 731-735, 2008.

[9]   Z-M Yuan, et al., “Perspectives of Magnetic Recording System at 10 Tb/in²,” FB-1, APMRC 2009, Grand Hyatt Hotel, Singapore, Jan. 14-16, 2009.

[10]           C. M. Cheong, et al., “Density Limit Estimation of Bit Patterned Media without Assisted Writing”, CP-10, Intermag, Sacramento, May 4-8 2009.

[11]           J. Zhu, 50th Ann. Conf. Magn. Magn. Mater. session CC-12 (2005)

[12]           X. Zhu and J. Zhu, Intermag 2006, Session EF-09.

[13]           J. Zhu, et al., “Microwave Assisted Magnetic Recording”, vol. 44, Jan 2008.

[14]           C.K. Goh, Z. Yuan and B. Liu,  “Microwave-Assisted Magnetic Recording at Lower Transverse Oscillating Field”, Conference Magnetism and Magnetic Materials, 2008

[15]           C.K. Goh, Z. Yuan and B. Liu, “Square Microwave-Assisted Magnetic Recording at Lower Frequencies”, APL 2009.

Microwave Assisted Magnetic Recording (MAMR)

2        Microwave Assisted Magnetic Recording

2.1       Literature

           

            The Microwave Assisted Magnetic Recording was first introduced by Professor Jimmy Zhu in 50^th Annual Conference Magnetism and Magnetic Materials (2005) [11]. The idea is to utilize the ferromagnetic resonance phenomena to help in magnetization reversal. Figure 2 shows the effective switching field with three difference writing angle. The switching field is relatively reduced for all range of external wave frequencies. For each writing angle, there has an optima ac field frequency at which minimum switching field threshold is smallest.

Cited from: J. Zhu, et al., IEEE Trans. Mag. Vol. 44, No. 1, Jan 2008

Figure 7

            The simulation do work well for MAMR, however the way to generate a localized as field in the microwave regime with amplitudes at kOe scale is needed in order to be practical. Local ac field generating scheme utilizing the SMT effect was proposed by Professor Jimmy Zhu in INTERMAG 2006 [12]. Figure 8 shows a proposed design of the ac field generator or spin-torque oscillator (STO). The generated ac field frequency is inversely proportional to the Magnetization saturation (Ms) of the field generation layer (FGL) while the strength of the generated ac field is proportional to it.

Cited from: J. Zhu, et al., IEEE Trans. Mag. Vol. 44, No. 1, Jan 2008

Figure 8

            The ferromagnetic resonance frequency is proportional to the anisotropy field of the material. For magnetic material with anisotropy field of 50 kOe, the ac field frequency generated by FGL required about 100 GHz in order able to reverse the magnetization.  Dr. Goh Chi Keong had proposed by using the square-wave external field to assist the magnetization reversal, lower frequency is required [15]. Further study by Dr. Goh found that lowered switching field can even achieved by just applying 1^st and 3^rd harmonic of the square-wave [14]. The comparison of lowered switching field between sine-wave, square-wave, and the 1^st and 3^rd harmonic microwave is shown in figure 9.

Cited from: C. K. Goh, MMM, 2008

Figure 9

2.2       Issues on MAMR

In order to increase areal densities, a corresponding increase in magnetic anisotropy is required to match the reduction of the grain size. The critical issues for the spin-torque oscillator (STO) is the Ku required for the FGL is about exponentially increase with the Hk of the media, as pictured in figure 10. Since the ac field strength (proportional to Ms of FGL) and the ac field frequency (proportional to Hk of FGL) should correspond increase with higher Hk media in use.

Figure 10

Heat Assisted Magnetic Recording (HAMR)

1        Heat Assisted Magnetic Recording

1.1       Literature

In view of superparamagnetism limit, the magnetic recording system has to deal with the tradeoff among the signal to noise ratio, thermal stability, and the head write ability. Just few years ago, magnetic recording is switched from longitudinal recording system to perpendicular magnetic recording (PMR) system to detain the superparamagnetism limit. The perpendicular recording system successfully delays the superparamagnetism limit by significantly improve the write ability of magnetic recording. This allowed using higher anisotropy media, which is to maintain the thermal stability of the magnetization of the smaller grains. Current product by PMR, areal density is achieved at about 350Gb/in². There are some works [1, 2, 3] reported that the PMR is able to push the areal density up to 1 Tb/in². But, however, above this areal density, PMR would again come to the superparamagnetism limit.

To further increase the areal density of magnetic recording above 1 Tb/in², energy assisted to write is required. Two major examples for energy assisted schemes have been proposed are Heat Assisted Magnetic Recording (HAMR), and Microwave Assisted Magnetic Recording (MAMR).

Cited from: M. H. Kryder, ”Future Magnetic Recording Technologies”, 2002

Figure 1

Figure 1 shows the schematic diagram of an HAMR recording system. In principal, HAMR is to use an external heating source to locally heat up the recording medium before write by the recording head. This heating up the medium is able to reduce the anisotropy (Ku) of the medium. The reduction of medium coercivity with medium temperature is shown in figure 2. The normal operation temperature in hard disk drive without the extra heating source is around 77^oC. For HAMR, the medium need to further heat up to the temperature about the Curie temperature (Tc) of the medium in order able to write. For example, Curie temperature for FePt L1_o phase thin-film is at about ~650K. Curie temperature is the critical temperature at which the medium magnetism and the medium anisotropy field vanish. Therefore, at medium Curie temperature, high anisotropy media able to be write by the inductive head. Then, the medium need to rapid cooling down to retain the magnetization orientation had been written.

Cited from: M. H. Kryder, Proceedings of the IEEE, vol 96, issue 11, 2008

Figure 2

            Another attraction of the HAMR is that a very high effective writing field gradient can be achieved with no required contribution from the magnetic character of the recording head.

1.2       Latest Status of HAMR

           

In APMRC Jan 2009, Seagate had reported HAMR work successfully in experiment which can record at a track width of ~50 nm and an areal densities of ~240 Gb/in2 on high coercivity FePt media [4]. The experiment is carry out in a system that using the high recording medium (FePt), and a recording head integrating a pole head and a heating source to heat the medium to its Curie point at where the data is desired to be recorded. The head was flown over the FePt media with a Curie point of 650 K rotating as 2700 RPM with a head-medium-spacing of ~10 nm. Laser with 830 nm wavelength focused to a spot size of ~120 nm. The data recorded by HAMR is shown by MFM image in figure 3.

Cited from: W.A. Challener, FB-2, APMRC 2009, Grand Hyatt Hotel, Singapore, Jan. 14-16, 2009.

Figure 3

1.3       Issues on HAMR

                    

                     The issues on HAMR can be classified into two major categories, optical issues and thermal issues. Optical issues for example, how to produce a nano-sized optical spot (< 20 nm) and with an efficiency high enough to heat the media to high temperature (300 ^oC). Furthermore, the way to even reduces the spot size to achieve even higher areal densities. Since, the media is heat up to high temperature, this bring out thermal issues. For example, whether the lubricant layer it is able to withstand the high temperature. Other than these two major issues, other issues like how to integrating the writing pole head and the laser source also needed to solve. Certainly, same with other energy assisted recording approach, high Ku magnetic media with small grain size is demanded to achieve high areal densities. All of these issues need to be solve in order for HAMR come into product state. Current research on FePt has Ku about 6-10 x 10⁷ erg/cc with Ms of about 1100 emu/cc and H_k of around 116 kOe and able achieves grain size of ~3 nm.

Optical Issues

            In HAMR, the diffraction limit is the major obstacle. In conventional far field optic, the diffraction limit for the full width half-maximum (FWHM) optical spot size d as estimated from scalar diffraction theory is

Where l is the wavelength and NA is the numerical aperture of the focusing lens. In order to have smaller spot size, the laser wavelength should be as short as possible and the NA should be as high as possible. The current available wavelength with laser diode is about 375 nm. The NA is the product of the sine of the half-angle of the focused cone of light and the refractive index of the medium in which the light is focused. Researcher has proposed a solid immersion lens (SIL) [5] in which the light is brought to a focus at the bottom surface of a hemispherical lens. This approach gives NA of 1.8. By SIL approach together with 375 nm available wavelength correspond to a focused spot size of 106 nm. However, this spot size is still far away from the 25 nm spot size necessary for achieving areal densities > Tb/in² in magnetic recording system.

            To achieve areal densities in Tb/in² range the spot size should reduce and in order the read-back signal is significant, the fly height (FH) should be low. Therefore, it is both necessary and natural to employ near field optic in HAMR. The near field optic makes use of apertures or antennas, or combination of both to overcome the diffraction limit. But, however it come another issue on the energy efficiency to transfer the heat to the medium with relative small spot size.

Thermal Issues

            Except optical issues, thermal issues for HAMR are also critical. Since the medium need to heat up above 300^oC, thermal effect on the medium and slider is still have a lot of uncertainty. The thermal issues on HAMR system can divide into two respects, thermal effect on slider and thermal effect on medium.

            Slider heat absorption can come from two channels: (1) laser absorption along the laser energy delivery structure built in the slider (since the HAMR recording head is an integrated head on the slider, when the laser energy is activated, part of the heat will be absorb by the slider); (2) the reflected laser heat from the medium (when the laser reach the medium, some energy is absorbed and some are reflected from medium). This laser-induced slider temperature rises will cause the sensor sensitivity changes, the slider deformation, and the magnetic head protrusion; furthermore, it will cause the fly height unstable [7]. Figure 4 shows the temperature changes of slider with different laser powers at different rotation speeds.

Cited from: B. X. Xu, et al.,JAP 99, 2006

Figure 4

            The recording disk use to record data is constructed by many layers. Instead of magnetic layer, the thermal effect on other layer for example lubricant layer, soft underlayer, and intermediate layer need to understand. These would seriously affect the recording disk robust and recording performance.

            Furthermore, the thermal gradient would cause the transition location changes along the track direction and cross-track direction. In addition, the thermal erasure on the neighboring tracks is another serious problem in HAMR. Dr. Xu Baosi has studied on the thermal profile in medium in order to study the heating effect on the medium [8]. Figure 5 shows the cross-track thermal profiles at 2000 rpm and 3000 rpm.

Cited from: B. X. Xu, et al., JMMM 320, pp. 731-735, 2008

Figure 5

1.5       Future Prospect

Combine with BPM

With current available material, HAMR alone is unable to achieve areal density above 10 Tb/in². Bit patterned media has predefined domains, as a medium it behaves as a single magnetic domain due to a strong coupling between the grains in a bit providing. Thus, BPM approach able to improve the thermal stability of the media. Current reports have shown that BPM able to achieve areal density to about 3 Tb/in² [9, 10]. Figure 6 shows the achievable areal density by BPM with considering difference thermal stability energy. Combination of HAMR with BPM is able to push areal density above 10 Tb/in².

Figure 6: Achievable areal density by BPM

about superconductivity

We know that superconductors provide three extraordinary powerful features - zero resistivity, perfect diamagnetic, and Josephson Effect, which are a vital enhancement of functionality in electrical, magnetic, and quantum mechanics fields, respectively.

Zero resistivity of a superconductor directly change the essential electrical relation of current, voltage and energy dissipation in a device, which will lead to a new era of revolution in electronics. Its bottomless benefits are still yet to be fully materialized. However, it definitely brings advantages in low energy consumption, power efficiency and even in device’s endurance. 

Superconducting magnetism is one of the most striking electromagnetic phenomena known. In superconducting state, a superconductor is perfectly diamagnetic where the interior of superconducting material expulses external magnetic field. This phenomenon (which is named Meissner effect) is deviated from the classical theory of ‘prefect conductor’. This characteristic is totally unexpected before the discovered of superconductor.

Superconductor is one of a few macroscopic materials that manifest quantum mechanics behaviors. Josephson Effect is a fascinating quantum tunneling phenomenon where supercurrent tunnels through an extremely thin insulator. This effect is currently being employed in the building block of SQUIDs. Josephson effect is also adopted by some high-end research like quantum computing and photon detection.

Despite having much discussed above, superconductors are still far from fully comprehensive. Particular properties of superconductor are still keeping discovering. The instances, the Tao effect, the de Heer effect, and the rotating superconductor. Last but foremost, superconductor brings new aspect of ideas, integrating different aspect of knowledge provides a wide range of innovation and invention, of for blinking science and technology progress.