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<div>Dear vega lew:
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Harmonic Transition State Theory (hTST) can help you to calculate the attempt frequency which can be obtained if the vibrational frequencies of the reactant and saddle-point states are known.
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Reference: H.Eyring, J.Chem.Phys. 3,107 (1935) (Or you can call it "quantum mechanically modified TST"). Its classical limit is the Vineyard form: G.H.Vineyard, J.Phys.Chem.Solids 3,121 (1957)
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However, the calculation of phonons maybe time consuming, so empirical values for attempt frequency should be prefered if you just want to make an estimation. The usually used attempt frequency range from 1.0*10^12 to 5.0*10^12 (or the optical mode frequency as prof. N. Marzari said). This should yield quite reasonable results because the jump frequency is just linearly proportional to the attempt frequency, and the jump frequency is exponentially dependent on the activation energy and temperature.
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And from the Arrhenius formula, an reaction event should not happen within several pico-seconds under 1000 K with E_ac=0.6 eV, and T>800 K should be required for the reaction with 0.2 eV. In order to estimate, you need just plot the Arrhenius formula in Gnuplot or Origin: v=v_attemp*exp(-11594E_ac/T) with E_ac in eV unit.
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Best Wishes!
<BR>
Yours Sincerely
<BR>
L.F.Huang
<BR>
<BR>
</FONT><FONT color=#444444>> From: vega lew
<BR>
</FONT><FONT color=#444444>> Subject: Re: [Pw_forum] one more question about NEB and CP
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</FONT><FONT color=#444444>> To: PWSCF Forum
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</FONT><FONT color=#444444>> Message-ID:
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</FONT><FONT color=#444444>>
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</FONT><FONT color=#444444>> Content-Type: text/plain; charset="iso-8859-1"
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</FONT><FONT color=#444444>>
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</FONT><FONT color=#444444>> Dear friends,
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</FONT><FONT color=#444444>>
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</FONT><FONT color=#444444>> thank you for all the help.
<BR>
</FONT><FONT color=#444444>>
<BR>
</FONT><FONT color=#444444>> I see arrhenius formula is suitable for my question. But I am wondering how
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</FONT><FONT color=#444444>> to determine the attempt rate for specific system?
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</FONT><FONT color=#444444>>
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</FONT><FONT color=#444444>> Do you think 300K is suitable for the reaction with activation energy of 0.2
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</FONT><FONT color=#444444>> eV?
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</FONT><FONT color=#444444>>
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</FONT><FONT color=#444444>> And in my case, the product state is lower than reactant state for about 0.4
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</FONT><FONT color=#444444>> eV, i.e. if the reaction happens, there is 0.6 eV barrier for
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</FONT><FONT color=#444444>> the product state to go back to the reactant state. Do you think the
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</FONT><FONT color=#444444>> dynamical equilibria of the reaction could see in some ps simulation
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</FONT><FONT color=#444444>> of pw.x?
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</FONT><FONT color=#444444>>
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</FONT><FONT color=#444444>> best wishes,
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</FONT><FONT color=#444444>>
<BR>
</FONT><FONT color=#444444>> vega
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</FONT><FONT color=#444444>>
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</FONT><FONT color=#444444>> On Mon, Nov 23, 2009 at 6:23 AM, Nicola Marzari wrote:
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</FONT><FONT color=#444444>>
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> vega lew wrote:
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> </FONT><FONT color=#444444>> Dear all,
<BR>
</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> >
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> </FONT><FONT color=#444444>> I used to perform NEB calculations to estimate the energy barrier for
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> </FONT><FONT color=#444444>> certain chemical reaction.
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> </FONT><FONT color=#444444>> The calculated activation barrier is about 0.2 eV. I want the see the
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> </FONT><FONT color=#444444>> reaction process during some pico-second of CP calculations.
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> </FONT><FONT color=#444444>> Do you think the reaction could happen in such a short time? and what
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> </FONT><FONT color=#444444>> temperature is suitable for jumping over the saddle point?
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> >
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> </FONT><FONT color=#444444>> thank you for reading
<BR>
</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> >
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> </FONT><FONT color=#444444>> best wishes,
<BR>
</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> >
<BR>
</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> </FONT><FONT color=#444444>> vega
<BR>
</FONT><FONT color=#444444>> >
<BR>
</FONT><FONT color=#444444>> >
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> Hi Vega,
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</FONT><FONT color=#444444>> >
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> try to work this out by yourself, looking at the arrhenius formula ; put an
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> attempt rate comparable to say an optical phonon. But the answer is
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> probably yes,
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> especially if you are a bit over room temperature (500-600K).
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</FONT><FONT color=#444444>> >
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> nicola
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</FONT><FONT color=#444444>> >
<BR>
</FONT><FONT color=#444444>> >
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> --
<BR>
</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> ---------------------------------------------------------------------
<BR>
</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> Prof Nicola Marzari Department of Materials Science and Engineering
<BR>
</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> 13-5066 MIT 77 Massachusetts Avenue Cambridge MA 02139-4307 USA
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> tel 617.4522758 fax 2586534 <A href=mailto:marzari@mit.edu>marzari@mit.edu</A</FONT><FONT color=#444444>> <A href=http://quasiamore.mit.edu target=_blank>http://quasiamore.mit.edu</A>
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</FONT><FONT color=#444444>> >
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</FONT><FONT color=#444444>> </FONT><FONT color=#444444>> _______________________________________________
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</FONT><FONT color=#444444>>
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</FONT><FONT color=#444444>> --
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</FONT><FONT color=#444444>> ==================================================================================
<BR>
</FONT><FONT color=#444444>> Vega Lew ( weijia liu)
<BR>
</FONT><FONT color=#444444>> Graduate student
<BR>
</FONT><FONT color=#444444>> State Key Laboratory of Materials-oriented Chemical Engineering
<BR>
</FONT><FONT color=#444444>> College of Chemistry and Chemical Engineering
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</FONT><FONT color=#444444>> Nanjing University of Technology, 210009, Nanjing, Jiangsu, China
<BR>
</FONT><FONT color=#444444>> ******************************************************************************************************************
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</FONT><FONT color=#444444>> Email: <A href=mailto:vegalew@gmail.com>vegalew@gmail.com</A>
<BR>
</FONT><FONT color=#444444>> Office: Room A705, Technical Innovation Building, Xinmofan Road 5#, Nanjing,
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</FONT><FONT color=#444444>> Jiangsu, China
<BR>
</FONT><FONT color=#444444>>
<BR>
<BR>
------
<BR>
======================================================================
<BR>
L.F.Huang(黄良锋) ph.D candidate, DFT and phonon physics
<BR>
======================================================================
<BR>
Add: Research Laboratory for Computational Materials Sciences,
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Instutue of Solid State Physics,the Chinese Academy of Sciences,
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P.O.Box 1129, Hefei 230031, P.R.China
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Tel: 86-551-5591464-328(office)
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Fax: 86-551-5591434
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Web: <A href=http://theory.issp.ac.cn target=_blank>http://theory.issp.ac.cn</A</FONT><FONT color=#444444>> (website of our theory group)
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<A href=http://www.issp.ac.cn target=_blank>http://www.issp.ac.cn</A</FONT><FONT color=#444444>> (website of our institute)
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======================================================================
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