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hao_jian木蟲 (正式寫手)
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[交流]
【求助】缺高角度數(shù)據(jù)怎么辦啊 已有2人參與
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我們的晶胞太大，經(jīng)常因為晶體太小，導致高角度點太弱，有個A類錯誤沒法解決，誰有高招，不勝感激：錯誤是： THETM01_ALERT_3_A The value of sine(theta_max)/wavelength is less than 0.550 Calculated sin(theta_max)/wavelength = 0.4999 測的晶體都不大，上機器測的都是好不容易找到的最大的單晶，但還不夠大。 增加衍射強度的方法也試過n次，要么背景太強，要么信號太弱。 我想知道有沒有什么后期處理的方式，把這個錯誤的影響降低，例如變成B類錯誤？ 按我們的經(jīng)驗，解的過程順，無需大量限制鍵長和溫度因子的數(shù)據(jù)都不錯。根據(jù)這個經(jīng)驗，上述數(shù)據(jù)解出來的結(jié)構(gòu)可信度非常好，由數(shù)據(jù)自然得到的鍵長和熱運動都非常符合常規(guī)，而無需增加額外的不自然的限制。 我們測的都是非常大的晶胞，R因子、Q峰、溫度因子等等要求都不是很高。 cif網(wǎng)站介紹此錯誤： PROC-NAME: THETM01 Type_3 PURPOSE: To check that _diffrn_reflns_theta_max is greater than expected limits. PROCEDURE: CALCULATE S = SIN [_diffrn_reflns_theta_max] / _diffrn_radiation_wavelength TEST IF S < 0.55 issue ALERT A "Alert A The value of sine(theta_max)/wavelength is less than 0.550" < 0.575 issue ALERT B "Alert B The value of sine(theta_max)/wavelength is less than 0.575" < 0.59 issue ALERT C "Alert C The value of sine(theta_max)/wavelength is less than 0.590" The Commission on Journals has determined that setting the maximum sin(theta)/lambda for measurements to at least 0.6 is both optimal and achievable for most structural studies. The extent of the data not only affects the ratio of measurements to refined parameters and hence the accuracy of the atomic and geometric parameters, but also the reliability of the angular dependent terms, such as Uijs. It is unlikely that any submitted CIF which contains the results of a data collection with a lower theta(max) will be accepted for publication unless there are exceptional circumstances. Old data claimed to have been collected when less stringent criteria were in place will not be excepted. You should routinely set your diffractometer so that a theta(max) of 25 deg. for Mo radiation or 67 deg. for Cu radiation is the minimum that is achieved. If the crystal diffracts sufficiently well, it is strongly recommended that theta(max) is set to an even higher value. It is understood that there may be little point in collecting background "noise" when a weakly diffracting crystal gives no detectable diffraction above theta values well below our required limit. In such a case, you should first ensure that you have conscientiously undertaken all possible steps to ensure that the experiment has been able to extract the best diffracting power from your sample. To this end, all of the following options should have been exhausted: (a) The best possible crystal has been sought and utilised for the data collection. If the crystal was small or of poor quality, are you sure that a better or bigger one cannot be obtained? The chosen crystal may have been the best one in the batch, but had enough effort and patience really been expended in the crystallisation attempt? Often, lack of experience, impatience or unwillingness to try another crystallisation technique or solvent leads to the experimentalist abandoning crystallisation attempts before the optimal conditions have been found. Before you blame the crystal quality, be sure that you have convinced yourself that nothing further can be done in this direction. (b) Use low temperature measurements to enhance the reflection intensities and the extent of the "observed" data. (c) For organic compounds, try data collection with Cu radiation, which significantly enhances the reflection intensities. [ Last edited by hao_jian on 2010-4-22 at 13:31 ] |
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鐵桿木蟲 (著名寫手)
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2樓2010-04-22 11:33:13
hao_jian
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帝夫:謝謝回帖交流 2010-04-24 14:36
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謝謝您的意見！ 晶體都不大，上機器測的都是好不容易找到的最大的單晶，但還不夠大。 增加衍射強度的方法也試過n次，要么背景太強，要么信號太弱。 我想知道有沒有什么后期處理的方式，把這個錯誤的影響降低，例如變成B類錯誤？ 按我們的經(jīng)驗，解的過程順，無需大量限制鍵長和溫度因子的數(shù)據(jù)都不錯。根據(jù)這個經(jīng)驗，上述數(shù)據(jù)解出來的結(jié)構(gòu)可信度非常好，由數(shù)據(jù)自然得到的鍵長和熱運動都非常符合常規(guī)，而無需增加額外的不自然的限制。 我們測的都是非常大的晶胞，R因子、Q峰、溫度因子等等要求都不是很高。 【這一段話已經(jīng)編輯加入1樓】 [ Last edited by hao_jian on 2010-4-22 at 13:38 ] |
3樓2010-04-22 13:19:00
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