I had read some theoretical paper about defect in GaN. They analysis the defect using formation energies as a function of Fermi level. If the formation energy is too big, this defect is very unlikely to be seen. So what does this “formation energy” mean? The formation energy is the energy required to produce a defect (a vacancy) into the perfect crystal structure.In the case of GaN, the formation energy of each defect is a function of the Fermi energy and the difference of the chemical potentials between Ga and N. The formation energy is the cost of creating a defect into an otherwise perfect solid. For a vacancy it is calculated as the energy needed to remove an atom from the bulk and take it to infinity. Formation energies are very important because the concentration of defects in a solid in thermodynamic equilibrium depends exponentially on it.
What's the differences among the concepts: binding energy, cohesive energy and formation energy?
Formation energy is the change in energy when a material is formed from it's constituent elements in their reference states. For example, the formation energy of alumina (Al2O3) is the change in energy when fcc aluminum and O2 gas combine to make Al2O3.
Cohesive energy is the amount of energy it takes to break something up into isolated atoms. This is also called the atomization energy.
Binding energy in general means the amount of energy to split something up, and can mean different things depending on the context. For example, if you're talking about a molecule, it can refer to atomization energy.
Something to keep in mind regarding sign conventions is that formation energies are typically given as negative values, whereas cohesive energies and binding energies are typically positive values.
The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the compound from its constituent elements, with all substances in their standard states at 1 atmosphere (1 atm or 101.3 kPa). Its symbol is ΔHfO or ΔfHO. The superscript theta (zero) on this symbol indicates that the process has occurred under standard conditions at the specified temperature (usually 25 degrees Celsius or 298.15 K). Standard states are as follows:
For a gas: the standard state is a pressure of exactly 1 atm
For a solute present in an ideal solution: a concentration of exactly one mole/liter (M) at a pressure of 1 atm
For a pure substance or a solvent in a condensed state (a liquid or a solid): the standard state is the pure liquid or solid under a pressure of 1 atm
For an element: the form in which the element is most stable under 1 atm of pressure. One exception is phosphorus, for which the most stable form at 1 atm is black phosphorus, but white phosphorus is chosen as the standard reference state for zero enthalpy of formation.[1]
For example, the standard enthalpy of formation of carbon dioxide would be the enthalpy of the following reaction under the conditions above:
C(s,graphite) + O2(g) → CO2(g)
All elements are written in their standard states, and one mole of product is formed. This is true for all enthalpies of formation.
The standard enthalpy of formation is measured in units of energy per amount of substance, usually stated in kilojoule per mole (kJ mol−1), but also in calorie per mole, joule per mole or kilocalorie per gram (any combination of these units conforming to the energy per mass or amount guideline). In physics the energy per particle is often expressed inelectronvolts which corresponds to about 100 kJ mol−1.
All elements in their standard states (oxygen gas, solid carbon in the form of graphite, etc.) have a standard enthalpy of formation of zero, as there is no change involved in their formation.
The formation reaction is a constant pressure and constant temperature process. Since the pressure of the standard formation reaction is fixed at 1 atm, the standard formation enthalpy or reaction heat is a function of temperature. For tabulation purposes, standard formation enthalpies are all given at a single temperature: 298 K, represented by the symbol ΔHf298O .
The standard enthalpy of formation is equivalent to the sum of many separate processes included in the Born-Haber cycle of synthesis reactions. For example, to calculate the standard enthalpy of formation of sodium chloride, we use the following reaction:
Na(s) + (1/2)Cl2(g) → NaCl(s)
This process is made of many separate sub-processes, each with its own enthalpy. Therefore, we must take into account:
The standard enthalpy of atomization of chlorine gas
The electron affinity of chlorine atoms
The lattice enthalpy of sodium chloride
The sum of all these values will give the standard enthalpy of formation of sodium chloride.
Additionally, applying Hess's Law shows that the sum of the individual reactions corresponding to the enthalpy change of formation for each substance in the reaction is equal to the enthalpy change of the overall reaction, regardless of the number of steps or intermediate reactions involved. This is because enthalpy is a state function. In the example above the standard enthalpy change of formation for sodium chloride is equal to the sum of the standard enthalpy change of formation for each of the steps involved in the process. This is especially useful for very long reactions with many intermediate steps and compounds.
Chemists may use standard enthalpies of formation for a reaction that is hypothetical. For instance carbon and hydrogen will not directly react to form methane, yet the standard enthalpy of formation for methane is determined to be −74.8 kJ mol−1 from using other known standard enthalpies of reaction with Hess's law. That it is negative shows that the reaction, if it were to proceed, would be exothermic; that is, it is enthalpically more stable than hydrogen gas and carbon.
It is possible to predict heat of formations for simple unstrained organic compounds with the Heat of formation group additivity method.
(State: g = gaseous; l = liquid; s = solid; aq = aqueous)
The Boltzmann constant has the dimensionenergy divided by temperature, the same as entropy. The accepted value in SI units is1.38064852(79)×10−23J/K.
Since k is a physical constant of proportionality between temperature and energy, its numerical value depends on the choice of units for energy and temperature. The small numerical value of the Boltzmann constant in SI units means a change in temperature by 1 K only changes a particle's energy by a small amount. A change of 1 °C is defined to be the same as a change of 1 K. The characteristic energy kT is a term encountered in many physical relationships.
Existing socialist parties in Europe did not wholly approve of the way
the Bolsheviks took power- and kept it. However, the possibility of a workers’
state fired people’s imagination across the world. In many countries, communist
parties were formed-like the Communist Party of Great Britain. The
Bolsheviks encouraged colonial peoples to follow their experiment. Many
non-Russians from outside the USSR participated in the Conference of the
Peoples of the East (1920) and the Bolshevik-founded Comintern (an
international union of pro-Bolshevik socialist parties). Some received
education in the USSR’s Communist University of the Workers of the East. By the
time of the outbreak of the Second World War, the USSR had given socialism a
global face and world stature.
Yet by the 1950s it was acknowledged within the country that the style
of government in the USSR was not in keeping with the ideals of the Russian
Revolution. In the world socialist movement too it was recognised that all was
not well in the Soviet Union. A backward country had become a great power. Its
industries and agriculture had developed and the poor were being fed. But it
had denied the essential freedoms to its citizens and carried out its
developmental projects through repressive policies. By the end of the twentieth
century, the international reputation of the USSR as a socialist country had
declined though it was recognised that socialist ideals still enjoyed respect
among its people. But in each country the ideas of socialism were rethought in
a variety of different ways. USSR and India:
Writing
about the Russian Revolution in India
Among those the Russian Revolution inspired were many Indians. Several attended
the Communist University. By the mid-1920s the Communist Party was formed in
India. Its members kept in touch with the Soviet Communist Party. Important
Indian political and cultural figures took an interest in the Soviet experiment
and visited Russia, among them Jawaharlal Nehru and Rabindranath Tagore, who
wrote about Soviet Socialism. In India, writings gave impressions of Soviet
Russia. In Hindi, R.S. Avasthi wrote in 1920-21 Russian Revolution, Lenin,
His Life and His Thoughts, and later The Red Revolution .
S.D. Vidyalankar wrote The Rebirth of Russia and The Soviet State of
Russia. There was much that was written in Bengali, Marathi, Malayalam,
Tamil and Telugu.
An
Indian arrives in Soviet Russia in 1920
‘For the first time in our lives, we were seeing Europeans mixing
freely with Asians. On seeing the Russians mingling freely with the rest of the
people of the country we were convinced that we had come to a land of real
equality.
We saw freedom in its true light. In spite of their poverty, imposed by
the counter-revolutionaries and the imperialists, the people were more jovial
and satisfied than ever before. The revolution had instilled confidence and
fearlessness in them. The real brotherhood of mankind would be seen here among
these people of fifty different nationalities. No barriers of caste or religion
hindered them from mixing freely with one another. Every soul was transformed
into an orator. One could see a worker, a peasant or a soldier haranguing like
a professional lecturer.’
Shaukat
Usmani,Historic Trips of a Revolutionary.
Rabindranath
Tagore wrote from Russia in 1930
‘Moscow appears much less clean than the other European capitals. None
of those hurrying along the streets look smart. The whole place belongs to the workers…
Here the masses have not in the least been
put in the shade by the gentlemen…those who lived in the background for
ages have come forward in the open today… I thought of the peasants and workers
in my own country. It all seemed like the work of the Genii in the Arabian
Nights. [here] only a decade ago they were as illiterate, helpless and hungry
as our own masses… Who could be more astonished than an unfortunate Indian like
myself to see how they had removed the mountain of ignorance and helplessness
in these few years.’
The Indo–Soviet
Treaty of Peace, Friendship and Cooperation was a treaty signed
between India and the Soviet Union in August 1971 that
specified mutual strategic cooperation. The treaty was a significant deviation
from India's previous position of non-alignment in the Cold
War and in the prelude to the Bangladesh war, it was a key
development in a situation of increasing Sino-American ties and American
pressure. The treaty was later adopted to the Indo-Bangladesh Treaty
of Friendship and cooperation in 1972.
The
Treaty
The Indo-Soviet Treaty of Peace, Friendship and Co-operation, 9 August
1971
Desirous of expanding and consolidating the existing relations of
sincere friendship between them,
The period of the early Planned Economy was linked to the disasters of the collectivisation of agriculture. By 1927- 1928, the towns in Soviet Russia were facing an acute problem of grain supplies. The government fixed prices at which grain must be sold, but the peasants refused to sell their grain to government buyers at these prices.
Stalin, who headed the party after the death of Lenin, introduced firm emergency measures. He believed that rich peasants and traders in the countryside were holding stocks in the hope of higher prices. Speculation had to be stopped and supplies confiscated. In 1928, Party members toured the grain-producing areas, supervising enforced grain collections, and raiding ‘kulaks’ - the name for well to- do peasants. As shortages continued, the decision was taken to collectivise farms. It was argued that grain shortages were partly due to the small size of holdings. After 1917, land had been given over to peasants. These small-sized peasant farms could not be modernised. To develop modern farms, and run them along industrial lines with machinery, it was necessary to ‘eliminate kulaks’, take away land from peasants, and establish state-controlled large farms.
What followed was Stalin’s collectivisation programme. From 1929, the Party forced all peasants to cultivate in collective farms (kolkhoz). The bulk of land and implements were transferred to the ownership of collective farms. Peasants worked on the land, and the kolkhozprofit was shared. Enraged peasants resisted the authorities anddestroyed their livestock. Between 1929 and 1931, the number ofcattle fell by one-third. Those who resisted collectivisation wereseverely punished. Many were deported (Forcibly removed from one’s own country) and exiled (Forced to live away from one.s own country). As they resistedcollectivisation, peasants argued that they were not rich and theywere not against socialism. They merely did not want to work incollective farms for a variety of reasons. Stalin’s government allowedsome independent cultivation, but treated such cultivatorsunsympathetically.
In spite of collectivisation, production did not increase immediately. In fact, the bad harvests of 1930-1933 led to one of most devastating famines in Soviet history when over 4 million died.
Many within the Party criticised the confusion in industrial production under the Planned Economy and the consequences of collectivisation. Stalin and his sympathisers charged these critics with conspiracy against socialism. Accusations were made throughout the country, and by 1939, over 2 million were in prisons or labour camps. Most were innocent of the crimes, but no one spoke for them. A large number were forced to make false confessions under torture and were executed . several among them were talented professionals.
Official view of the opposition to collectivisation and the government response
‘From the second half of February of this year, in various regions of the Ukraine …..mass insurrections of the peasantry have taken place, caused by distortions of the Party’s line by a section of the lower ranks of the Party and the Soviet apparatus in the course of the introduction of collectivisation and preparatory work for the spring harvest.
Within a short time, large scale activities from the above-mentioned regions carried over into neighbouring areas- and the most aggressive insurrections have taken place near the border.
The greater part of the peasant insurrections have been linked with outright demands for the return of collectivised stocks of grain, livestock and tools…
Between 1st February and 15th March, 25,000 have been arrested…. 656 have been executed, 3673 have been imprisoned in labour camps and 5580 exiled….’
Report of K.M. Karlson, President of the State Police Administration of the Ukraine
to the Central Committee of the Communist Party, on 19 March 1930.
From: V. Sokolov (ed), Obshchestvo I Vlast, v 1930-ye gody
This is a letter written by a peasant who did not want to join the collective farm.
To the newspaper Krestianskaia Gazeta(Peasant Newspaper)
‘.. I am a natural working peasant born in 1879… there are 6 members in my family, my wife was born in 1881, my son is 16, two daughters 19, all three go to school, my sister is 71. From 1932, heavy taxes have been levied on me that I have found impossible. From 1935, local authorities have increased the taxes on me… and I was unable to handle them and all my property was registered:
my horse, cow, calf, sheep with lambs, all my implements, furniture and my reserve of wood for repair of buildings and they sold the lot for the taxes. In 1936, they sold two of my buildings… the kolkhoz bought them. In 1937, of two huts I had, one was sold and one was confiscated ..’
Afanasii Dedorovich Frebenev, an independent cultivator.
From: V. Sokolov (ed), Obshchestvo I Vlast, v 1930-ye gody.
During the civil war,
the Bolsheviks kept industries and banks nationalised. They permitted peasants
to cultivate the land that had been socialised. Bolsheviks used confiscated
land to demonstrate what collective work could be.
A process of centralised
planning was introduced. Officials assessed how the economy could work and set
targets for a five-year period. On this basis they made the Five Year Plans.
The government fixed all prices to promote industrial growth during the first
two ‘Plans’(1927-1932 and 1933-1938).
In 1928 the New
Economic Policy was replaced with a Five
Year Plan. Stalin argued that 'either we do it, or we are crushed,' as
Soviet industry lagged well behind the Western European states in terms of productivity
and qality. The Five Year Plans created targets for all sectors of Industry.
These were set and monitored by central government with a view to improving the
industrial capacity of the Soviet Union. The Industrial targets involved heavy
investment in mining and the extraction of raw materials from Russia's vast
interior. It required massive movement of workers to sites designated as being
primae areas for production of specific items and it meant an end to profit
based prodction in factories and on farms. Farming also changed as part of this
policy. From 1928 onwards farming was collectivised.
This involved closing small holdings and combining them into massive,
mechanised farms that were state controled. These should be more efficient,
would lead to better education, training and use of technology and were
intended to increase productivity and efficiency. Ideologicaly they were also
more in line with socialism as the benefits of the new system would be felt by
all.
Centralised planning led
to economic growth. Industrial production increased (between 1929 and 1933 by 100 per cent in the case
of oil, coal and steel). New factory cities came into being. However, rapid
construction led to poor working conditions. In the city of Magnitogorsk, the construction of a
steel plant was achieved in three years. Workers lived hard lives and the
result was 550 stoppages of work in the first year alone. In living quarters, ‘in
the wintertime, at 40 degrees below, people had to climb down from the fourth
floor and dash across the street in order to go to the toilet’.
An extended schooling
system developed, and arrangements were made for factory workers and peasants
to enter universities. Crèches were established in factories for the children
of women workers. Cheap public health care
was provided. Model living quarters were set up for workers. The effect of all
this was uneven, though, since government resources were limited.
Socialist Cultivation in a
Village in the Ukraine
'A commune was set up
using two [confiscated] farms as a base. The commune consisted of thirteen
families with a total of seventy persons..... The farm tools taken from the.... farms were turned over to the commune.....The members ate in a communal dining
hall and income was divided in accordance with the principles of "cooperative communism".
The entire proceeds of the members' labor, as well as all dwellings and facilities
belonging to the commune were shared by the commune members'.
Fedor Belov, The History of a Soviet Collective Farm (1955).
Dreams and Realities of a
Soviet Childhood in 1933
Dear grandfather Kalinin…..
My family is large, there are four
children. We don.t have a father- he died, fighting for the worker’s cause, and
my mother…. is ailing…. I want to study very much, but I cannot go to school. I
had some old boots, but they are completely torn and no one can mend them. My
mother is sick, we have no money and no bread, but I want to study very much. …..there
stands before us the task of studying, studying and studying. That is what
Vladimir Ilich Lenin said. But I have to stop going to school. We have no
relatives and there is no one to help us, so I have to go to work in a factory,
to prevent the family from starving. Dear grandfather, I am 13, I study well and
have no bad reports. I am in Class 5…..
Letter of 1933 from a 13-year-old worker to Kalinin, Soviet
President
From:V. Sokolov (ed), Obshchestvo I Vlast, v 1930-ye gody
(Moscow, 1997). Reference:
