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   Atomic units (au) form a system of units convenient for atomic physics, electromagnetism and quantum electrodynamics. There are two different kinds of atomic units, which one might mane Hartree atomic units and Rydberg atomic units, which differ in the choice of unit of the mass and charge.

a. Hartree atomic units.
   This atomic units is based on the following definition:

The name Système International d'Unités (International System of Units)) with the international abbreviation SI is a single international language of science and technology first introduced in 1960. SI is a coherent system based on the seven independent physical quantities (base units) and derived quantities (derived units). Note that since 1995 supplementary units have been abandoned and moved into the class of derived SI units.

Other physical quantities are derived from the basic units. The derived SI units are obtained by the multiplication, division, integration and differentiation of the basic units without the introduction of any numerical factors. The system of units so derived is said to be coherent.

Length: metre (m)

Mass: kilogram (kg)

Time: second (s)

Electric current: ampere (A)

Thermodynamic temperature: kelvin (K)

In addition to the thermodynamic temperature (symbol T) there is also the Celsius (symbol t) defined by the equation t=T-T₀ where T₀=273.15 K. Celsius temperature is expressed in degree Celsius (symbol C). The unit 'degree Celsius' is equal to the unit 'kelvin', and a temperature interval or a difference of temperature may also be expressed in degrees Celsius. (The word degree and the sign ^o must not be used with kelvin or K).

Amount of substance: mole (mol)

When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles or specified groups of such particle.

In this definition, it is understood that the carbon 12 atoms are unbound, at rest and in their ground state.

Luminous intensity: candela (cd)

Plane angle: radian (rad) and solid angle: steradian (sr)

The radian and steradian were classified as supplementary units.

At the time of the introduction of the International System, the question of the nature of these supplementary units was left open. Considering that plane angle is generally expressed as the ratio between two lengths and solid angle as the ratio between an area and the square or a length, it was specified that in the International System the quantities plane angle and solid angle should be considered as dimensionless derived quantities. Therefore, the supplementary units radian and steradian are to be regarded as dimensionless derived units which may be used or omitted in the expressions for derived units.

Since October , 1995, the class of supplementary units as a separate class in the SI has been removed. Thus the SI now consists of only two classes of units: base units and derived units, with the radian and steradian, which were the two supplementary units, moved into the class of SI derived units.

DFT??? What is it? It stands for Density Functional Theory.

"Density functional theory is a quantum mechanical theory used in physics and chemistry to investigate the ground state of many-body system, in particular atoms, molecules and the condensed phases. It is among the most popular and versatile methods available in condensed matter physics, computational physics and conputational chemistry."

Now I am using DFT in my researches everyday but I do not understand it really deeply. I think that it is quite difficult to understand all stuffs inside itself and in applying it in real calculations.

However, the important thing is that although you do not understand it really deeply, assumming that you do understand it, you can use it in your researches via some commercial and non-commercial codes using DTF.

Nowaday people can do many things with DFT. It is one of the most powerful method in condensed matter theory, computational physics, computational material and computational chemistry.

If you are interested in DFT I can suggest you some materials about it. Maybe the best paper is Nobel Lecture: Electronic structure of matter-wave functions and density functionals written by Walter Kohn, who won Nobel prize for his contributions to DFT. If you can not get this material (because you need to pay for it), you can have an another nice introducing to DTF freely from Kieron Burke and his friends from: http://dft.rutgers.edu/kieron/beta.

About books on DFT, I think the best ones are "Electronic Structure: Basic Theory and Pracical Methods" written by R. Martin and "Electronic Structure Calculations for Solids and Molecules: Theory and Computational Methods" written by J. Kohanoff. The first one is really a kind of "dictionary" of DFT and quite difficult because it contains everything and the later is a practical oriented book on DFT and it is easier to read than the first one. There is also one excellent book you can read online: "Density-Functional theory of Atoms and Molecules" written by Robert G. Parr and Weitao Yang. You can read it via Google book here: Google book.

    Question: What is the difference between theoretical physics and mathematical physics?

    Answer: Theoretical physics is done by physicists who lack the necessary skills to do real experiments, mathematical physics is done by mathematicians who lack the necessary skills to do real mathematics.

   I am a theoretical physicist so according to Mermin what can I do ???

user guide

bands.x

cppp.x

d3.x

dos.x

ld1.x

ph.x

pp.x

projwfc.x

pw.x

pwcond.x

Primitive vectors: a1 = a/ 2 (y + z)/2 a2 = a/ 2 (z + x)/2 a3 = a/ 2 (x + y)/2 Reciprocal lattice: b1 = 4 π / a (y + z - x)/2 b2 = 4 π / a (z + x - y)/2 b3 = 4 π / a (x + y - z)/2

 

Label	Cartesian Coordinates	Lattice Coordinates	Range
Γ	( 0 , 0 , 0 )	0	Point
Δ	( 0 , x , 0 )	½ x (b1 + b3)	0 < x < 1
X	( 0 , 1 , 0 )	½(b1 + b3)	Point
Z	( x/2 , 1 , 0 )	½b1 + ¼ x b2 + ¼ (2+x) b3	0 < x < 1
W	( 1/2 , 1 , 0 )	½b1 + ¼ b2 + ¾ b3	Point
Q	( 1/2 , 1 - x /2 , x/2 )	½ b1 + ¼ (1 + x) b2+ ¼ (3 - x) b3	0 < x < 1
L	( 1/2 , 1/2 , 1/2 )	½b1 + ½ b2 + ½ b3	Point
Λ	( x /2 , x /2 , x /2 )	½ x b1 + ½ x b2 + ½ x b3	1 > x > 0
Γ	( 0 , 0 , 0 )	0	Point
Σ	( x , x , 0 )	½ x b1 + ½ x b2 + x b3	0 < x < 3/4
K = U	( 3/4 , 3/4 , 0 )	3/8 b1 + 3/8 b2 + ¾ b3	Point
S	( x , x , 0 )	½ x b1 + ½ x b2 + x b3	3/4 < x < 1
X'	( 1 , 1 , 0 )	½ b1 + ½ b2 + b3	Point
W-K line	( (2+x)/4 , (4-x)/4 ,0 )	(½ - x/8) b1 + (¼ + x/8) b2 + ¾ b3	0 < x < 1
K-L line	( (3-x)/4 , (3-x)/4 , x/2 )	(3+x)/8 b1 + (3+x)/8 b2 + (3-x)/4 b3	0 < x < 1

Primitive vectors: a1 = a/ 2 (y + z - x)/2 a2 = a/ 2 (z + x - y)/2 a3 = a/ 2 (x + y - z)/2 Reciprocal lattice: b1 = 4 π / a (y + z)/2 b2 = 4 π / a (z + x)/2 b3 = 4 π / a (x + y)/2

Label	Cartesian Coordinates	Lattice Coordinates	Range
Γ	( 0 , 0 , 0 )	(0,0,0)	Point
Δ	( x , 0 , 0 )	(-x/2,x/2,x/2)	0 < x < 1
H	( 1 , 0 , 0 )	(-1/2,1/2,1/2)	Point
F	( x , 1-x , 1-x )	(1-3x/2,x/2,x/2)	1 > x > 1/2
P	( 1/2 , 1/2 , 1/2 )	(1/4,1/4,1/4)	Point
D	( 1/2 , 1/2 , x )	(x/2,x/2,(1-x)/2)	1/2 > x > 0
N	( 1/2 , 1/2 , 0 )	(0,0,1/2)	Point
Σ	( x , x , 0 )	(0,0,x)	1/2 > x > 0
Γ	( 0 , 0 , 0 )	(0,0,0)	Point
Λ	( x , x , x )	(x/2,x/2,x/2)	0 < x < 1/2
P	( 1/2 , 1/2 , 1/2 )	(1/4,1/4,1/4)	Point

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