c*******o
发帖数: 1722 | 1 okay, i can give you an example but dunno if it is a good or even correct
one.
when i was in tsinghua, in my department, there is a prof. doing ion beam
interaction with materials. he used to use a lot thermal dynamics to explain
his results but people just wont agree with him. so, he started to use
computer simulations, given an ion ion or ion electron potential, solve all
interactions between ion and ion or ion electron, so on so forth. people call
it melacular dynamics. the prof. said it is a | i***p
发帖数: 14 | 2 I can not agree.
first principle means start from basic assumption
without any approximation, derive the final result.
sometime, it is complete impossible to do it for a realistic
problem, so now, some people say first principle, they mean:
start from a few basic idea about the system you are considering,
take as less as possible approximations as possible.
but you can still imagine the result could vary with the
assumptions and approximations.
so I think, first principle means start from the ba
【在 c*******o 的大作中提到】
: okay, i can give you an example but dunno if it is a good or even correct
: one.
: when i was in tsinghua, in my department, there is a prof. doing ion beam
: interaction with materials. he used to use a lot thermal dynamics to explain
: his results but people just wont agree with him. so, he started to use
: computer simulations, given an ion ion or ion electron potential, solve all
: interactions between ion and ion or ion electron, so on so forth. people call
: it melacular dynamics. the prof. said it is a
| x*****r
发帖数: 5 | 3 I also can not agree what you said.
Many modern approaches for ab-initio calculations of atoms, molecules, liquids
and solids are based on density functional theory. Basically, there are two
steps to be done: the Hohenberg-Kohn theorem supplies a rigorous theoretical
treatment; the Kohn-Sham equations then result in an iterative approach for
actual calculations. In density functional theoryl, the role of the electron
wave function is replaced by the charge density. In order to solve the
exchang
【在 i***p 的大作中提到】
: I can not agree.
: first principle means start from basic assumption
: without any approximation, derive the final result.
: sometime, it is complete impossible to do it for a realistic
: problem, so now, some people say first principle, they mean:
: start from a few basic idea about the system you are considering,
: take as less as possible approximations as possible.
: but you can still imagine the result could vary with the
: assumptions and approximations.
: so I think, first principle means start from the ba
| s***a
发帖数: 7 | 4 if you mean "ab initio" in computational science. it basically means that you
start from schrodinger equation.and don't use any emperical things.
for example, if you want to do molecular dynamics to a ion-electron system.
let's set ions as classical particles ( of course in some meaning this
treatment
is not "ab initio") then you need to solve the equation : mx''=-dV. if you
treat
dv as the empirical interaction among the ions then it is not first principle,
but if you solve dv from the schrodin |
|
